From e0de8d98214d514d1e120bdcf1b72d03899e04e2 Mon Sep 17 00:00:00 2001 From: Bruce Momjian Date: Sat, 29 Dec 2001 03:42:59 +0000 Subject: [PATCH] Update FAQ_DEV. --- doc/FAQ_DEV | 681 ++++++++++++++-------------- doc/src/FAQ/FAQ_DEV.html | 956 ++++++++++++++++++++------------------- 2 files changed, 827 insertions(+), 810 deletions(-) diff --git a/doc/FAQ_DEV b/doc/FAQ_DEV index d5faef76a0..073a3917a1 100644 --- a/doc/FAQ_DEV +++ b/doc/FAQ_DEV @@ -9,31 +9,146 @@ postgreSQL Web site, http://www.PostgreSQL.org. _________________________________________________________________ - Questions + General Questions - 1) What tools are available for developers? - 2) What books are good for developers? - 3) Why do we use palloc() and pfree() to allocate memory? - 4) Why do we use Node and List to make data structures? - 5) How do I add a feature or fix a bug? - 6) How do I download/update the current source tree? - 7) How do I test my changes? - 7) I just added a field to a structure. What else should I do? - 8) Why are table, column, type, function, view names sometimes + 1.1) How do I get involved in PostgreSQL development? + 1.2) How do I add a feature or fix a bug? + 1.3) How do I download/update the current source tree? + 1.4) How do I test my changes? + 1.5) What tools are available for developers? + 1.6) What books are good for developers? + 1.7) What is configure all about? + 1.8) How do I add a new port? + 1.9) Why don't we use threads in the backend? + 1.10) How are RPM's packaged? + 1.11) How are CVS branches handled? + +Technical Questions + + 2.1) How do I efficiently access information in tables from the + backend code? + 2.2) Why are table, column, type, function, view names sometimes referenced as Name or NameData, and sometimes as char *? - 9) How do I efficiently access information in tables from the backend - code? - 10) What is elog()? - 11) What is configure all about? - 12) How do I add a new port? - 13) What is CommandCounterIncrement()? - 14) Why don't we use threads in the backend? - 15) How are RPM's packaged? - 16) How are CVS branches handled? - 17) How do I get involved in PostgreSQL development? + 2.3) Why do we use Node and List to make data structures? + 2.4) I just added a field to a structure. What else should I do? + 2.5) Why do we use palloc() and pfree() to allocate memory? + 2.6) What is elog()? + 2.7) What is CommandCounterIncrement()? _________________________________________________________________ - 1) What tools are available for developers? + General Questions + + 1.1) How go I get involved in PostgreSQL development? + + This was written by Lamar Owen: + + 2001-06-22 + What open source development process is used by the PostgreSQL team? + + Read HACKERS for six months (or a full release cycle, whichever is + longer). Really. HACKERS _is_the process. The process is not well + documented (AFAIK -- it may be somewhere that I am not aware of) -- + and it changes continually. + What development environment (OS, system, compilers, etc) is required + to develop code? + + Developers Corner on the website has links to this information. The + distribution tarball itself includes all the extra tools and documents + that go beyond a good Unix-like development environment. In general, a + modern unix with a modern gcc, GNU make or equivalent, autoconf (of a + particular version), and good working knowledge of those tools are + required. + What areas need support? + + The TODO list. + + You've made the first step, by finding and subscribing to HACKERS. + Once you find an area to look at in the TODO, and have read the + documentation on the internals, etc, then you check out a current + CVS,write what you are going to write (keeping your CVS checkout up to + date in the process), and make up a patch (as a context diff only) and + send to the PATCHES list, prefereably. + + Discussion on the patch typically happens here. If the patch adds a + major feature, it would be a good idea to talk about it first on the + HACKERS list, in order to increase the chances of it being accepted, + as well as toavoid duplication of effort. Note that experienced + developers with a proven track record usually get the big jobs -- for + more than one reason. Also note that PostgreSQL is highly portable -- + nonportable code will likely be dismissed out of hand. + + Once your contributions get accepted, things move from there. + Typically, you would be added as a developer on the list on the + website when one of the other developers recommends it. Membership on + the steering committee is by invitation only, by the other steering + committee members, from what I have gathered watching froma distance. + + I make these statements from having watched the process for over two + years. + + To see a good example of how one goes about this, search the archives + for the name 'Tom Lane' and see what his first post consisted of, and + where he took things. In particular, note that this hasn't been _that_ + long ago -- and his bugfixing and general deep knowledge with this + codebase is legendary. Take a few days to read after him. And pay + special attention to both the sheer quantity as well as the + painstaking quality of his work. Both are in high demand. + + 1.2) How do I add a feature or fix a bug? + + The source code is over 250,000 lines. Many problems/features are + isolated to one specific area of the code. Others require knowledge of + much of the source. If you are confused about where to start, ask the + hackers list, and they will be glad to assess the complexity and give + pointers on where to start. + + Another thing to keep in mind is that many fixes and features can be + added with surprisingly little code. I often start by adding code, + then looking at other areas in the code where similar things are done, + and by the time I am finished, the patch is quite small and compact. + + When adding code, keep in mind that it should use the existing + facilities in the source, for performance reasons and for simplicity. + Often a review of existing code doing similar things is helpful. + + 1.3) How do I download/update the current source tree? + + There are several ways to obtain the source tree. Occasional + developers can just get the most recent source tree snapshot from + ftp.postgresql.org. For regular developers, you can use CVS. CVS + allows you to download the source tree, then occasionally update your + copy of the source tree with any new changes. Using CVS, you don't + have to download the entire source each time, only the changed files. + Anonymous CVS does not allows developers to update the remote source + tree, though privileged developers can do this. There is a CVS FAQ on + our web site that describes how to use remote CVS. You can also use + CVSup, which has similarly functionality, and is available from + ftp.postgresql.org. + + To update the source tree, there are two ways. You can generate a + patch against your current source tree, perhaps using the make_diff + tools mentioned above, and send them to the patches list. They will be + reviewed, and applied in a timely manner. If the patch is major, and + we are in beta testing, the developers may wait for the final release + before applying your patches. + + For hard-core developers, Marc(scrappy@postgresql.org) will give you a + Unix shell account on postgresql.org, so you can use CVS to update the + main source tree, or you can ftp your files into your account, patch, + and cvs install the changes directly into the source tree. + + 1.4) How do I test my changes? + + First, use psql to make sure it is working as you expect. Then run + src/test/regress and get the output of src/test/regress/checkresults + with and without your changes, to see that your patch does not change + the regression test in unexpected ways. This practice has saved me + many times. The regression tests test the code in ways I would never + do, and has caught many bugs in my patches. By finding the problems + now, you save yourself a lot of debugging later when things are + broken, and you can't figure out when it happened. + + 1.5) What tools are available for developers? Aside from the User documentation mentioned in the regular FAQ, there are several development tools available. First, all the files in the @@ -126,264 +241,32 @@ */ pgindent will the format code by specifying flags to your operating - system's utility indent. - - pgindent is run on all source files just before each beta test period. - It auto-formats all source files to make them consistent. Comment - blocks that need specific line breaks should be formatted as block - comments, where the comment starts as /*------. These comments will - not be reformatted in any way. - - pginclude contains scripts used to add needed #include's to include - files, and removed unneeded #include's. - - When adding system types, you will need to assign oids to them. There - is also a script called unused_oids in pgsql/src/include/catalog that - shows the unused oids. - - 2) What books are good for developers? - - I have four good books, An Introduction to Database Systems, by C.J. - Date, Addison, Wesley, A Guide to the SQL Standard, by C.J. Date, et. - al, Addison, Wesley, Fundamentals of Database Systems, by Elmasri and - Navathe, and Transaction Processing, by Jim Gray, Morgan, Kaufmann - - There is also a database performance site, with a handbook on-line - written by Jim Gray at http://www.benchmarkresources.com. - - 3) Why do we use palloc() and pfree() to allocate memory? - - palloc() and pfree() are used in place of malloc() and free() because - we automatically free all memory allocated when a transaction - completes. This makes it easier to make sure we free memory that gets - allocated in one place, but only freed much later. There are several - contexts that memory can be allocated in, and this controls when the - allocated memory is automatically freed by the backend. - - 4) Why do we use Node and List to make data structures? - - We do this because this allows a consistent way to pass data inside - the backend in a flexible way. Every node has a NodeTag which - specifies what type of data is inside the Node. Lists are groups of - Nodes chained together as a forward-linked list. - - Here are some of the List manipulation commands: - - lfirst(i) - return the data at list element i. - - lnext(i) - return the next list element after i. - - foreach(i, list) - loop through list, assigning each list element to i. It is - important to note that i is a List *, not the data in the List - element. You need to use lfirst(i) to get at the data. Here is - a typical code snipped that loops through a List containing Var - *'s and processes each one: - -List *i, *list; - - foreach(i, list) - { - Var *var = lfirst(i); - - /* process var here */ - } - - lcons(node, list) - add node to the front of list, or create a new list with node - if list is NIL. - - lappend(list, node) - add node to the end of list. This is more expensive that lcons. - - nconc(list1, list2) - Concat list2 on to the end of list1. - - length(list) - return the length of the list. - - nth(i, list) - return the i'th element in list. - - lconsi, ... - There are integer versions of these: lconsi, lappendi, nthi. - List's containing integers instead of Node pointers are used to - hold list of relation object id's and other integer quantities. - - You can print nodes easily inside gdb. First, to disable output - truncation when you use the gdb print command: -(gdb) set print elements 0 - - Instead of printing values in gdb format, you can use the next two - commands to print out List, Node, and structure contents in a verbose - format that is easier to understand. List's are unrolled into nodes, - and nodes are printed in detail. The first prints in a short format, - and the second in a long format: -(gdb) call print(any_pointer) - (gdb) call pprint(any_pointer) - - The output appears in the postmaster log file, or on your screen if - you are running a backend directly without a postmaster. - - 5) How do I add a feature or fix a bug? - - The source code is over 250,000 lines. Many problems/features are - isolated to one specific area of the code. Others require knowledge of - much of the source. If you are confused about where to start, ask the - hackers list, and they will be glad to assess the complexity and give - pointers on where to start. - - Another thing to keep in mind is that many fixes and features can be - added with surprisingly little code. I often start by adding code, - then looking at other areas in the code where similar things are done, - and by the time I am finished, the patch is quite small and compact. - - When adding code, keep in mind that it should use the existing - facilities in the source, for performance reasons and for simplicity. - Often a review of existing code doing similar things is helpful. - - 6) How do I download/update the current source tree? - - There are several ways to obtain the source tree. Occasional - developers can just get the most recent source tree snapshot from - ftp.postgresql.org. For regular developers, you can use CVS. CVS - allows you to download the source tree, then occasionally update your - copy of the source tree with any new changes. Using CVS, you don't - have to download the entire source each time, only the changed files. - Anonymous CVS does not allows developers to update the remote source - tree, though privileged developers can do this. There is a CVS FAQ on - our web site that describes how to use remote CVS. You can also use - CVSup, which has similarly functionality, and is available from - ftp.postgresql.org. - - To update the source tree, there are two ways. You can generate a - patch against your current source tree, perhaps using the make_diff - tools mentioned above, and send them to the patches list. They will be - reviewed, and applied in a timely manner. If the patch is major, and - we are in beta testing, the developers may wait for the final release - before applying your patches. - - For hard-core developers, Marc(scrappy@postgresql.org) will give you a - Unix shell account on postgresql.org, so you can use CVS to update the - main source tree, or you can ftp your files into your account, patch, - and cvs install the changes directly into the source tree. - - 6) How do I test my changes? - - First, use psql to make sure it is working as you expect. Then run - src/test/regress and get the output of src/test/regress/checkresults - with and without your changes, to see that your patch does not change - the regression test in unexpected ways. This practice has saved me - many times. The regression tests test the code in ways I would never - do, and has caught many bugs in my patches. By finding the problems - now, you save yourself a lot of debugging later when things are - broken, and you can't figure out when it happened. - - 7) I just added a field to a structure. What else should I do? - - The structures passing around from the parser, rewrite, optimizer, and - executor require quite a bit of support. Most structures have support - routines in src/backend/nodes used to create, copy, read, and output - those structures. Make sure you add support for your new field to - these files. Find any other places the structure may need code for - your new field. mkid is helpful with this (see above). - - 8) Why are table, column, type, function, view names sometimes referenced as - Name or NameData, and sometimes as char *? - - Table, column, type, function, and view names are stored in system - tables in columns of type Name. Name is a fixed-length, - null-terminated type of NAMEDATALEN bytes. (The default value for - NAMEDATALEN is 32 bytes.) -typedef struct nameData - { - char data[NAMEDATALEN]; - } NameData; - typedef NameData *Name; - - Table, column, type, function, and view names that come into the - backend via user queries are stored as variable-length, - null-terminated character strings. - - Many functions are called with both types of names, ie. heap_open(). - Because the Name type is null-terminated, it is safe to pass it to a - function expecting a char *. Because there are many cases where - on-disk names(Name) are compared to user-supplied names(char *), there - are many cases where Name and char * are used interchangeably. - - 9) How do I efficiently access information in tables from the backend code? - - You first need to find the tuples(rows) you are interested in. There - are two ways. First, SearchSysCache() and related functions allow you - to query the system catalogs. This is the preferred way to access - system tables, because the first call to the cache loads the needed - rows, and future requests can return the results without accessing the - base table. The caches use system table indexes to look up tuples. A - list of available caches is located in - src/backend/utils/cache/syscache.c. - src/backend/utils/cache/lsyscache.c contains many column-specific - cache lookup functions. - - The rows returned are cache-owned versions of the heap rows. - Therefore, you must not modify or delete the tuple returned by - SearchSysCache(). What you should do is release it with - ReleaseSysCache() when you are done using it; this informs the cache - that it can discard that tuple if necessary. If you neglect to call - ReleaseSysCache(), then the cache entry will remain locked in the - cache until end of transaction, which is tolerable but not very - desirable. - - If you can't use the system cache, you will need to retrieve the data - directly from the heap table, using the buffer cache that is shared by - all backends. The backend automatically takes care of loading the rows - into the buffer cache. - - Open the table with heap_open(). You can then start a table scan with - heap_beginscan(), then use heap_getnext() and continue as long as - HeapTupleIsValid() returns true. Then do a heap_endscan(). Keys can be - assigned to the scan. No indexes are used, so all rows are going to be - compared to the keys, and only the valid rows returned. - - You can also use heap_fetch() to fetch rows by block number/offset. - While scans automatically lock/unlock rows from the buffer cache, with - heap_fetch(), you must pass a Buffer pointer, and ReleaseBuffer() it - when completed. - - Once you have the row, you can get data that is common to all tuples, - like t_self and t_oid, by merely accessing the HeapTuple structure - entries. If you need a table-specific column, you should take the - HeapTuple pointer, and use the GETSTRUCT() macro to access the - table-specific start of the tuple. You then cast the pointer as a - Form_pg_proc pointer if you are accessing the pg_proc table, or - Form_pg_type if you are accessing pg_type. You can then access the - columns by using a structure pointer: -((Form_pg_class) GETSTRUCT(tuple))->relnatts - - You must not directly change live tuples in this way. The best way is - to use heap_modifytuple() and pass it your original tuple, and the - values you want changed. It returns a palloc'ed tuple, which you pass - to heap_replace(). You can delete tuples by passing the tuple's t_self - to heap_destroy(). You use t_self for heap_update() too. Remember, - tuples can be either system cache copies, which may go away after you - call ReleaseSysCache(), or read directly from disk buffers, which go - away when you heap_getnext(), heap_endscan, or ReleaseBuffer(), in the - heap_fetch() case. Or it may be a palloc'ed tuple, that you must - pfree() when finished. + system's utility indent. + + pgindent is run on all source files just before each beta test period. + It auto-formats all source files to make them consistent. Comment + blocks that need specific line breaks should be formatted as block + comments, where the comment starts as /*------. These comments will + not be reformatted in any way. + + pginclude contains scripts used to add needed #include's to include + files, and removed unneeded #include's. + + When adding system types, you will need to assign oids to them. There + is also a script called unused_oids in pgsql/src/include/catalog that + shows the unused oids. - 10) What is elog()? + 1.6) What books are good for developers? - elog() is used to send messages to the front-end, and optionally - terminate the current query being processed. The first parameter is an - elog level of NOTICE, DEBUG, ERROR, or FATAL. NOTICE prints on the - user's terminal and the postmaster logs. DEBUG prints only in the - postmaster logs. ERROR prints in both places, and terminates the - current query, never returning from the call. FATAL terminates the - backend process. The remaining parameters of elog are a printf-style - set of parameters to print. + I have four good books, An Introduction to Database Systems, by C.J. + Date, Addison, Wesley, A Guide to the SQL Standard, by C.J. Date, et. + al, Addison, Wesley, Fundamentals of Database Systems, by Elmasri and + Navathe, and Transaction Processing, by Jim Gray, Morgan, Kaufmann + + There is also a database performance site, with a handbook on-line + written by Jim Gray at http://www.benchmarkresources.com. - 11) What is configure all about? + 1.7) What is configure all about? The files configure and configure.in are part of the GNU autoconf package. Configure allows us to test for various capabilities of the @@ -405,7 +288,7 @@ typedef struct nameData removed, so you see only the file contained in the source distribution. - 12) How do I add a new port? + 1.8) How do I add a new port? There are a variety of places that need to be modified to add a new port. First, start in the src/template directory. Add an appropriate @@ -422,19 +305,7 @@ typedef struct nameData src/makefiles directory for port-specific Makefile handling. There is a backend/port directory if you need special files for your OS. - 13) What is CommandCounterIncrement()? - - Normally, transactions can not see the rows they modify. This allows - UPDATE foo SET x = x + 1 to work correctly. - - However, there are cases where a transactions needs to see rows - affected in previous parts of the transaction. This is accomplished - using a Command Counter. Incrementing the counter allows transactions - to be broken into pieces so each piece can see rows modified by - previous pieces. CommandCounterIncrement() increments the Command - Counter, creating a new part of the transaction. - - 14) Why don't we use threads in the backend? + 1.9) Why don't we use threads in the backend? There are several reasons threads are not used: * Historically, threads were unsupported and buggy. @@ -443,7 +314,7 @@ typedef struct nameData remaining backend startup time. * The backend code would be more complex. - 15) How are RPM's packaged? + 1.10) How are RPM's packaged? This was written by Lamar Owen: @@ -538,7 +409,7 @@ typedef struct nameData Of course, there are many projects that DO include all the files necessary to build RPMs from their Official Tarball (TM). - 16) How are CVS branches managed? + 1.11) How are CVS branches managed? This was written by Tom Lane: @@ -597,58 +468,194 @@ typedef struct nameData tree right away after a major release --- we wait for a dot-release or two, so that we won't have to double-patch the first wave of fixes. - 17) How go I get involved in PostgreSQL development? + Technical Questions + + 2.1) How do I efficiently access information in tables from the backend code? - This was written by Lamar Owen: + You first need to find the tuples(rows) you are interested in. There + are two ways. First, SearchSysCache() and related functions allow you + to query the system catalogs. This is the preferred way to access + system tables, because the first call to the cache loads the needed + rows, and future requests can return the results without accessing the + base table. The caches use system table indexes to look up tuples. A + list of available caches is located in + src/backend/utils/cache/syscache.c. + src/backend/utils/cache/lsyscache.c contains many column-specific + cache lookup functions. - 2001-06-22 - What open source development process is used by the PostgreSQL team? + The rows returned are cache-owned versions of the heap rows. + Therefore, you must not modify or delete the tuple returned by + SearchSysCache(). What you should do is release it with + ReleaseSysCache() when you are done using it; this informs the cache + that it can discard that tuple if necessary. If you neglect to call + ReleaseSysCache(), then the cache entry will remain locked in the + cache until end of transaction, which is tolerable but not very + desirable. - Read HACKERS for six months (or a full release cycle, whichever is - longer). Really. HACKERS _is_the process. The process is not well - documented (AFAIK -- it may be somewhere that I am not aware of) -- - and it changes continually. - What development environment (OS, system, compilers, etc) is required - to develop code? + If you can't use the system cache, you will need to retrieve the data + directly from the heap table, using the buffer cache that is shared by + all backends. The backend automatically takes care of loading the rows + into the buffer cache. - Developers Corner on the website has links to this information. The - distribution tarball itself includes all the extra tools and documents - that go beyond a good Unix-like development environment. In general, a - modern unix with a modern gcc, GNU make or equivalent, autoconf (of a - particular version), and good working knowledge of those tools are - required. - What areas need support? + Open the table with heap_open(). You can then start a table scan with + heap_beginscan(), then use heap_getnext() and continue as long as + HeapTupleIsValid() returns true. Then do a heap_endscan(). Keys can be + assigned to the scan. No indexes are used, so all rows are going to be + compared to the keys, and only the valid rows returned. - The TODO list. + You can also use heap_fetch() to fetch rows by block number/offset. + While scans automatically lock/unlock rows from the buffer cache, with + heap_fetch(), you must pass a Buffer pointer, and ReleaseBuffer() it + when completed. - You've made the first step, by finding and subscribing to HACKERS. - Once you find an area to look at in the TODO, and have read the - documentation on the internals, etc, then you check out a current - CVS,write what you are going to write (keeping your CVS checkout up to - date in the process), and make up a patch (as a context diff only) and - send to the PATCHES list, prefereably. + Once you have the row, you can get data that is common to all tuples, + like t_self and t_oid, by merely accessing the HeapTuple structure + entries. If you need a table-specific column, you should take the + HeapTuple pointer, and use the GETSTRUCT() macro to access the + table-specific start of the tuple. You then cast the pointer as a + Form_pg_proc pointer if you are accessing the pg_proc table, or + Form_pg_type if you are accessing pg_type. You can then access the + columns by using a structure pointer: +((Form_pg_class) GETSTRUCT(tuple))->relnatts + + You must not directly change live tuples in this way. The best way is + to use heap_modifytuple() and pass it your original tuple, and the + values you want changed. It returns a palloc'ed tuple, which you pass + to heap_replace(). You can delete tuples by passing the tuple's t_self + to heap_destroy(). You use t_self for heap_update() too. Remember, + tuples can be either system cache copies, which may go away after you + call ReleaseSysCache(), or read directly from disk buffers, which go + away when you heap_getnext(), heap_endscan, or ReleaseBuffer(), in the + heap_fetch() case. Or it may be a palloc'ed tuple, that you must + pfree() when finished. - Discussion on the patch typically happens here. If the patch adds a - major feature, it would be a good idea to talk about it first on the - HACKERS list, in order to increase the chances of it being accepted, - as well as toavoid duplication of effort. Note that experienced - developers with a proven track record usually get the big jobs -- for - more than one reason. Also note that PostgreSQL is highly portable -- - nonportable code will likely be dismissed out of hand. + 2.2) Why are table, column, type, function, view names sometimes referenced + as Name or NameData, and sometimes as char *? + + Table, column, type, function, and view names are stored in system + tables in columns of type Name. Name is a fixed-length, + null-terminated type of NAMEDATALEN bytes. (The default value for + NAMEDATALEN is 32 bytes.) +typedef struct nameData + { + char data[NAMEDATALEN]; + } NameData; + typedef NameData *Name; + + Table, column, type, function, and view names that come into the + backend via user queries are stored as variable-length, + null-terminated character strings. - Once your contributions get accepted, things move from there. - Typically, you would be added as a developer on the list on the - website when one of the other developers recommends it. Membership on - the steering committee is by invitation only, by the other steering - committee members, from what I have gathered watching froma distance. + Many functions are called with both types of names, ie. heap_open(). + Because the Name type is null-terminated, it is safe to pass it to a + function expecting a char *. Because there are many cases where + on-disk names(Name) are compared to user-supplied names(char *), there + are many cases where Name and char * are used interchangeably. - I make these statements from having watched the process for over two - years. + 2.3) Why do we use Node and List to make data structures? + + We do this because this allows a consistent way to pass data inside + the backend in a flexible way. Every node has a NodeTag which + specifies what type of data is inside the Node. Lists are groups of + Nodes chained together as a forward-linked list. - To see a good example of how one goes about this, search the archives - for the name 'Tom Lane' and see what his first post consisted of, and - where he took things. In particular, note that this hasn't been _that_ - long ago -- and his bugfixing and general deep knowledge with this - codebase is legendary. Take a few days to read after him. And pay - special attention to both the sheer quantity as well as the - painstaking quality of his work. Both are in high demand. + Here are some of the List manipulation commands: + + lfirst(i) + return the data at list element i. + + lnext(i) + return the next list element after i. + + foreach(i, list) + loop through list, assigning each list element to i. It is + important to note that i is a List *, not the data in the List + element. You need to use lfirst(i) to get at the data. Here is + a typical code snipped that loops through a List containing Var + *'s and processes each one: + +List *i, *list; + + foreach(i, list) + { + Var *var = lfirst(i); + + /* process var here */ + } + + lcons(node, list) + add node to the front of list, or create a new list with node + if list is NIL. + + lappend(list, node) + add node to the end of list. This is more expensive that lcons. + + nconc(list1, list2) + Concat list2 on to the end of list1. + + length(list) + return the length of the list. + + nth(i, list) + return the i'th element in list. + + lconsi, ... + There are integer versions of these: lconsi, lappendi, nthi. + List's containing integers instead of Node pointers are used to + hold list of relation object id's and other integer quantities. + + You can print nodes easily inside gdb. First, to disable output + truncation when you use the gdb print command: +(gdb) set print elements 0 + + Instead of printing values in gdb format, you can use the next two + commands to print out List, Node, and structure contents in a verbose + format that is easier to understand. List's are unrolled into nodes, + and nodes are printed in detail. The first prints in a short format, + and the second in a long format: +(gdb) call print(any_pointer) + (gdb) call pprint(any_pointer) + + The output appears in the postmaster log file, or on your screen if + you are running a backend directly without a postmaster. + + 2.4) I just added a field to a structure. What else should I do? + + The structures passing around from the parser, rewrite, optimizer, and + executor require quite a bit of support. Most structures have support + routines in src/backend/nodes used to create, copy, read, and output + those structures. Make sure you add support for your new field to + these files. Find any other places the structure may need code for + your new field. mkid is helpful with this (see above). + + 2.5) Why do we use palloc() and pfree() to allocate memory? + + palloc() and pfree() are used in place of malloc() and free() because + we automatically free all memory allocated when a transaction + completes. This makes it easier to make sure we free memory that gets + allocated in one place, but only freed much later. There are several + contexts that memory can be allocated in, and this controls when the + allocated memory is automatically freed by the backend. + + 2.6) What is elog()? + + elog() is used to send messages to the front-end, and optionally + terminate the current query being processed. The first parameter is an + elog level of NOTICE, DEBUG, ERROR, or FATAL. NOTICE prints on the + user's terminal and the postmaster logs. DEBUG prints only in the + postmaster logs. ERROR prints in both places, and terminates the + current query, never returning from the call. FATAL terminates the + backend process. The remaining parameters of elog are a printf-style + set of parameters to print. + + 2.7) What is CommandCounterIncrement()? + + Normally, transactions can not see the rows they modify. This allows + UPDATE foo SET x = x + 1 to work correctly. + + However, there are cases where a transactions needs to see rows + affected in previous parts of the transaction. This is accomplished + using a Command Counter. Incrementing the counter allows transactions + to be broken into pieces so each piece can see rows modified by + previous pieces. CommandCounterIncrement() increments the Command + Counter, creating a new part of the transaction. diff --git a/doc/src/FAQ/FAQ_DEV.html b/doc/src/FAQ/FAQ_DEV.html index 07f63e3a86..2d00bdc5ca 100644 --- a/doc/src/FAQ/FAQ_DEV.html +++ b/doc/src/FAQ/FAQ_DEV.html @@ -27,39 +27,169 @@
-

Questions

+

General Questions

- 1) What tools are available for developers?
- 2) What books are good for developers?
- 3) Why do we use palloc() and - pfree() to allocate memory?
- 4) Why do we use Node and List to - make data structures?
- 5) How do I add a feature or fix a bug?
- 6) How do I download/update the current source + 1.1) How do I get involved in PostgreSQL + development?
+ 1.2) How do I add a feature or fix a bug?
+ 1.3) How do I download/update the current source tree?
- 7) How do I test my changes?
- 7) I just added a field to a structure. What else - should I do?
- 8) Why are table, column, type, function, view + 1.4) How do I test my changes?
+ 1.5) What tools are available for developers?
+ 1.6) What books are good for developers?
+ 1.7) What is configure all about?
+ 1.8) How do I add a new port?
+ 1.9) Why don't we use threads in the backend?
+ 1.10) How are RPM's packaged?
+ 1.11) How are CVS branches handled?
+ +

Technical Questions

+ 2.1) How do I efficiently access information in + tables from the backend code?
+ 2.2) Why are table, column, type, function, view names sometimes referenced as Name or NameData, and sometimes as char *?
- 9) How do I efficiently access information in - tables from the backend code?
- 10) What is elog()?
- 11) What is configure all about?
- 12) How do I add a new port?
- 13) What is CommandCounterIncrement()?
- 14) Why don't we use threads in the backend?
- 15) How are RPM's packaged?
- 16) How are CVS branches handled?
- 17) How do I get involved in PostgreSQL - development?
+ 2.3) Why do we use Node and List to + make data structures?
+ 2.4) I just added a field to a structure. What else + should I do?
+ 2.5) Why do we use palloc() and + pfree() to allocate memory?
+ 2.6) What is elog()?
+ 2.7) What is CommandCounterIncrement()?

-

1) What tools are available for +
+

General Questions

+
+ +

1.1) How go I get involved in PostgreSQL + development?

+ +

This was written by Lamar Owen:

+ +

2001-06-22

+ + What open source development process is used by the PostgreSQL + team? + +

Read HACKERS for six months (or a full release cycle, whichever + is longer). Really. HACKERS _is_the process. The process is not + well documented (AFAIK -- it may be somewhere that I am not aware + of) -- and it changes continually.

+ + What development environment (OS, system, compilers, etc) is + required to develop code? + +

Developers Corner on the + website has links to this information. The distribution tarball + itself includes all the extra tools and documents that go beyond a + good Unix-like development environment. In general, a modern unix + with a modern gcc, GNU make or equivalent, autoconf (of a + particular version), and good working knowledge of those tools are + required.

+ + What areas need support? + +

The TODO list.

+ +

You've made the first step, by finding and subscribing to + HACKERS. Once you find an area to look at in the TODO, and have + read the documentation on the internals, etc, then you check out a + current CVS,write what you are going to write (keeping your CVS + checkout up to date in the process), and make up a patch (as a + context diff only) and send to the PATCHES list, prefereably.

+ +

Discussion on the patch typically happens here. If the patch + adds a major feature, it would be a good idea to talk about it + first on the HACKERS list, in order to increase the chances of it + being accepted, as well as toavoid duplication of effort. Note that + experienced developers with a proven track record usually get the + big jobs -- for more than one reason. Also note that PostgreSQL is + highly portable -- nonportable code will likely be dismissed out of + hand.

+ +

Once your contributions get accepted, things move from there. + Typically, you would be added as a developer on the list on the + website when one of the other developers recommends it. Membership + on the steering committee is by invitation only, by the other + steering committee members, from what I have gathered watching + froma distance.

+ +

I make these statements from having watched the process for over + two years.

+ +

To see a good example of how one goes about this, search the + archives for the name 'Tom Lane' and see what his first post + consisted of, and where he took things. In particular, note that + this hasn't been _that_ long ago -- and his bugfixing and general + deep knowledge with this codebase is legendary. Take a few days to + read after him. And pay special attention to both the sheer + quantity as well as the painstaking quality of his work. Both are + in high demand.

+ +

1.2) How do I add a feature or fix a bug?

+ +

The source code is over 250,000 lines. Many problems/features + are isolated to one specific area of the code. Others require + knowledge of much of the source. If you are confused about where to + start, ask the hackers list, and they will be glad to assess the + complexity and give pointers on where to start.

+ +

Another thing to keep in mind is that many fixes and features + can be added with surprisingly little code. I often start by adding + code, then looking at other areas in the code where similar things + are done, and by the time I am finished, the patch is quite small + and compact.

+ +

When adding code, keep in mind that it should use the existing + facilities in the source, for performance reasons and for + simplicity. Often a review of existing code doing similar things is + helpful.

+ +

1.3) How do I download/update the current source + tree?

+ +

There are several ways to obtain the source tree. Occasional + developers can just get the most recent source tree snapshot from + ftp.postgresql.org. For regular developers, you can use CVS. CVS + allows you to download the source tree, then occasionally update + your copy of the source tree with any new changes. Using CVS, you + don't have to download the entire source each time, only the + changed files. Anonymous CVS does not allows developers to update + the remote source tree, though privileged developers can do this. + There is a CVS FAQ on our web site that describes how to use remote + CVS. You can also use CVSup, which has similarly functionality, and + is available from ftp.postgresql.org.

+ +

To update the source tree, there are two ways. You can generate + a patch against your current source tree, perhaps using the + make_diff tools mentioned above, and send them to the patches list. + They will be reviewed, and applied in a timely manner. If the patch + is major, and we are in beta testing, the developers may wait for + the final release before applying your patches.

+ +

For hard-core developers, Marc(scrappy@postgresql.org) will give + you a Unix shell account on postgresql.org, so you can use CVS to + update the main source tree, or you can ftp your files into your + account, patch, and cvs install the changes directly into the + source tree.

+ +

1.4) How do I test my changes?

+ +

First, use psql to make sure it is working as you expect. + Then run src/test/regress and get the output of + src/test/regress/checkresults with and without your changes, + to see that your patch does not change the regression test in + unexpected ways. This practice has saved me many times. The + regression tests test the code in ways I would never do, and has + caught many bugs in my patches. By finding the problems now, you + save yourself a lot of debugging later when things are broken, and + you can't figure out when it happened.

+ +

1.5) What tools are available for developers?

Aside from the User documentation mentioned in the regular FAQ, @@ -179,7 +309,7 @@ There is also a script called unused_oids in pgsql/src/include/catalog that shows the unused oids.

-

2) What books are good for developers?

+

1.6) What books are good for developers?

I have four good books, An Introduction to Database Systems, by C.J. Date, Addison, Wesley, A Guide to the SQL @@ -192,207 +322,245 @@ on-line written by Jim Gray at http://www.benchmarkresources.com.

-

3) Why do we use palloc() and - pfree() to allocate memory?

+

1.7) What is configure all about?

-

palloc() and pfree() are used in place of malloc() - and free() because we automatically free all memory allocated when - a transaction completes. This makes it easier to make sure we free - memory that gets allocated in one place, but only freed much later. - There are several contexts that memory can be allocated in, and - this controls when the allocated memory is automatically freed by - the backend.

+

The files configure and configure.in are part of + the GNU autoconf package. Configure allows us to test for + various capabilities of the OS, and to set variables that can then + be tested in C programs and Makefiles. Autoconf is installed on the + PostgreSQL main server. To add options to configure, edit + configure.in, and then run autoconf to generate + configure.

-

4) Why do we use Node and List to - make data structures?

+

When configure is run by the user, it tests various OS + capabilities, stores those in config.status and + config.cache, and modifies a list of *.in files. For + example, if there exists a Makefile.in, configure generates + a Makefile that contains substitutions for all @var@ + parameters found by configure.

-

We do this because this allows a consistent way to pass data - inside the backend in a flexible way. Every node has a - NodeTag which specifies what type of data is inside the - Node. Lists are groups of Nodes chained together as a - forward-linked list.

+

When you need to edit files, make sure you don't waste time + modifying files generated by configure. Edit the *.in + file, and re-run configure to recreate the needed file. If + you run make distclean from the top-level source directory, + all files derived by configure are removed, so you see only the + file contained in the source distribution.

-

Here are some of the List manipulation commands:

+

1.8) How do I add a new port?

-
-
-
lfirst(i)
+

There are a variety of places that need to be modified to add a + new port. First, start in the src/template directory. Add an + appropriate entry for your OS. Also, use src/config.guess to + add your OS to src/template/.similar. You shouldn't match + the OS version exactly. The configure test will look for an + exact OS version number, and if not found, find a match without + version number. Edit src/configure.in to add your new OS. + (See configure item above.) You will need to run autoconf, or patch + src/configure too.

-
return the data at list element i.
+

Then, check src/include/port and add your new OS file, + with appropriate values. Hopefully, there is already locking code + in src/include/storage/s_lock.h for your CPU. There is also + a src/makefiles directory for port-specific Makefile + handling. There is a backend/port directory if you need + special files for your OS.

-
lnext(i)
+

1.9) Why don't we use threads in the + backend?

-
return the next list element after i.
+

There are several reasons threads are not used:

-
foreach(i, list)
+
    +
  • Historically, threads were unsupported and buggy.
    • -
    - loop through list, assigning each list element to - i. It is important to note that i is a List *, - not the data in the List element. You need to use - lfirst(i) to get at the data. Here is a typical code - snipped that loops through a List containing Var *'s - and processes each one: -
    -List *i, *list;
-    
-    foreach(i, list)
-    {
-        Var *var = lfirst(i);
+      
  • An error in one backend can corrupt other backends.
    • 
 
-        /* process var here */
-    }
-    
-
    -
    +
  • Speed improvements using threads are small compared to the + remaining backend startup time.
    • -
    lcons(node, list)
    +
  • The backend code would be more complex.
    • +
-
add node to the front of list, or create a - new list with node if list is NIL.
+

1.10) How are RPM's packaged?

-
lappend(list, node)
+

This was written by Lamar Owen:

-
add node to the end of list. This is more - expensive that lcons.
+

2001-05-03

-
nconc(list1, list2)
+

As to how the RPMs are built -- to answer that question sanely + requires me to know how much experience you have with the whole RPM + paradigm. 'How is the RPM built?' is a multifaceted question. The + obvious simple answer is that I maintain:

-
Concat list2 on to the end of list1.
+
    +
  1. A set of patches to make certain portions of the source tree + 'behave' in the different environment of the RPMset;
    2. -
    length(list)
    +
  2. The initscript;
    3. -
    return the length of the list.
    +
  3. Any other ancilliary scripts and files;
    4. -
    nth(i, list)
    +
  4. A README.rpm-dist document that tries to adequately document + both the differences between the RPM build and the WHY of the + differences, as well as useful RPM environment operations (like, + using syslog, upgrading, getting postmaster to start at OS boot, + etc);
    5. -
    return the i'th element in list.
    +
  5. The spec file that throws it all together. This is not a + trivial undertaking in a package of this size.
    6. +
-
lconsi, ...
+

I then download and build on as many different canonical + distributions as I can -- currently I am able to build on Red Hat + 6.2, 7.0, and 7.1 on my personal hardware. Occasionally I receive + opportunity from certain commercial enterprises such as Great + Bridge and PostgreSQL, Inc. to build on other distributions.

-
There are integer versions of these: lconsi, lappendi, - nthi. List's containing integers instead of Node - pointers are used to hold list of relation object id's and - other integer quantities.
-
-
- You can print nodes easily inside gdb. First, to disable - output truncation when you use the gdb print command: -
-(gdb) set print elements 0
-
-
- Instead of printing values in gdb format, you can use the next two - commands to print out List, Node, and structure contents in a - verbose format that is easier to understand. List's are unrolled - into nodes, and nodes are printed in detail. The first prints in a - short format, and the second in a long format: -
-(gdb) call print(any_pointer)
-    (gdb) call pprint(any_pointer)
-
-
- The output appears in the postmaster log file, or on your screen if - you are running a backend directly without a postmaster. +

I test the build by installing the resulting packages and + running the regression tests. Once the build passes these tests, I + upload to the postgresql.org ftp server and make a release + announcement. I am also responsible for maintaining the RPM + download area on the ftp site.

-

5) How do I add a feature or fix a bug?

+

You'll notice I said 'canonical' distributions above. That + simply means that the machine is as stock 'out of the box' as + practical -- that is, everything (except select few programs) on + these boxen are installed by RPM; only official Red Hat released + RPMs are used (except in unusual circumstances involving software + that will not alter the build -- for example, installing a newer + non-RedHat version of the Dia diagramming package is OK -- + installing Python 2.1 on the box that has Python 1.5.2 installed is + not, as that alters the PostgreSQL build). The RPM as uploaded is + built to as close to out-of-the-box pristine as is possible. Only + the standard released 'official to that release' compiler is used + -- and only the standard official kernel is used as well.

-

The source code is over 250,000 lines. Many problems/features - are isolated to one specific area of the code. Others require - knowledge of much of the source. If you are confused about where to - start, ask the hackers list, and they will be glad to assess the - complexity and give pointers on where to start.

+

For a time I built on Mandrake for RedHat consumption -- no + more. Nonstandard RPM building systems are worse than useless. + Which is not to say that Mandrake is useless! By no means is + Mandrake useless -- unless you are building Red Hat RPMs -- and Red + Hat is useless if you're trying to build Mandrake or SuSE RPMs, for + that matter. But I would be foolish to use 'Lamar Owen's Super + Special RPM Blend Distro 0.1.2' to build for public consumption! + :-)

-

Another thing to keep in mind is that many fixes and features - can be added with surprisingly little code. I often start by adding - code, then looking at other areas in the code where similar things - are done, and by the time I am finished, the patch is quite small - and compact.

+

I _do_ attempt to make the _source_ RPM compatible with as many + distributions as possible -- however, since I have limited + resources (as a volunteer RPM maintainer) I am limited as to the + amount of testing said build will get on other distributions, + architectures, or systems.

-

When adding code, keep in mind that it should use the existing - facilities in the source, for performance reasons and for - simplicity. Often a review of existing code doing similar things is - helpful.

+

And, while I understand people's desire to immediately upgrade + to the newest version, realize that I do this as a side interest -- + I have a regular, full-time job as a broadcast + engineer/webmaster/sysadmin/Technical Director which occasionally + prevents me from making timely RPM releases. This happened during + the early part of the 7.1 beta cycle -- but I believe I was pretty + much on the ball for the Release Candidates and the final + release.

-

6) How do I download/update the current source - tree?

+

I am working towards a more open RPM distribution -- I would + dearly love to more fully document the process and put everything + into CVS -- once I figure out how I want to represent things such + as the spec file in a CVS form. It makes no sense to maintain a + changelog, for instance, in the spec file in CVS when CVS does a + better job of changelogs -- I will need to write a tool to generate + a real spec file from a CVS spec-source file that would add version + numbers, changelog entries, etc to the result before building the + RPM. IOW, I need to rethink the process -- and then go through the + motions of putting my long RPM history into CVS one version at a + time so that version history information isn't lost.

-

There are several ways to obtain the source tree. Occasional - developers can just get the most recent source tree snapshot from - ftp.postgresql.org. For regular developers, you can use CVS. CVS - allows you to download the source tree, then occasionally update - your copy of the source tree with any new changes. Using CVS, you - don't have to download the entire source each time, only the - changed files. Anonymous CVS does not allows developers to update - the remote source tree, though privileged developers can do this. - There is a CVS FAQ on our web site that describes how to use remote - CVS. You can also use CVSup, which has similarly functionality, and - is available from ftp.postgresql.org.

+

As to why all these files aren't part of the source tree, well, + unless there was a large cry for it to happen, I don't believe it + should. PostgreSQL is very platform-agnostic -- and I like that. + Including the RPM stuff as part of the Official Tarball (TM) would, + IMHO, slant that agnostic stance in a negative way. But maybe I'm + too sensitive to that. I'm not opposed to doing that if that is the + consensus of the core group -- and that would be a sneaky way to + get the stuff into CVS :-). But if the core group isn't thrilled + with the idea (and my instinct says they're not likely to be), I am + opposed to the idea -- not to keep the stuff to myself, but to not + hinder the platform-neutral stance. IMHO, of course.

-

To update the source tree, there are two ways. You can generate - a patch against your current source tree, perhaps using the - make_diff tools mentioned above, and send them to the patches list. - They will be reviewed, and applied in a timely manner. If the patch - is major, and we are in beta testing, the developers may wait for - the final release before applying your patches.

+

Of course, there are many projects that DO include all the files + necessary to build RPMs from their Official Tarball (TM).

-

For hard-core developers, Marc(scrappy@postgresql.org) will give - you a Unix shell account on postgresql.org, so you can use CVS to - update the main source tree, or you can ftp your files into your - account, patch, and cvs install the changes directly into the - source tree.

+

1.11) How are CVS branches managed?

-

6) How do I test my changes?

+

This was written by Tom Lane:

-

First, use psql to make sure it is working as you expect. - Then run src/test/regress and get the output of - src/test/regress/checkresults with and without your changes, - to see that your patch does not change the regression test in - unexpected ways. This practice has saved me many times. The - regression tests test the code in ways I would never do, and has - caught many bugs in my patches. By finding the problems now, you - save yourself a lot of debugging later when things are broken, and - you can't figure out when it happened.

+

2001-05-07

-

7) I just added a field to a structure. What - else should I do?

+

If you just do basic "cvs checkout", "cvs update", "cvs commit", + then you'll always be dealing with the HEAD version of the files in + CVS. That's what you want for development, but if you need to patch + past stable releases then you have to be able to access and update + the "branch" portions of our CVS repository. We normally fork off a + branch for a stable release just before starting the development + cycle for the next release.

-

The structures passing around from the parser, rewrite, - optimizer, and executor require quite a bit of support. Most - structures have support routines in src/backend/nodes used - to create, copy, read, and output those structures. Make sure you - add support for your new field to these files. Find any other - places the structure may need code for your new field. mkid - is helpful with this (see above).

+

The first thing you have to know is the branch name for the + branch you are interested in getting at. To do this, look at some + long-lived file, say the top-level HISTORY file, with "cvs status + -v" to see what the branch names are. (Thanks to Ian Lance Taylor + for pointing out that this is the easiest way to do it.) Typical + branch names are:

+
+    REL7_1_STABLE
+    REL7_0_PATCHES
+    REL6_5_PATCHES
+
-

8) Why are table, column, type, function, view - names sometimes referenced as Name or NameData, and - sometimes as char *?

+

OK, so how do you do work on a branch? By far the best way is to + create a separate checkout tree for the branch and do your work in + that. Not only is that the easiest way to deal with CVS, but you + really need to have the whole past tree available anyway to test + your work. (And you *better* test your work. Never forget that + dot-releases tend to go out with very little beta testing --- so + whenever you commit an update to a stable branch, you'd better be + doubly sure that it's correct.)

-

Table, column, type, function, and view names are stored in - system tables in columns of type Name. Name is a - fixed-length, null-terminated type of NAMEDATALEN bytes. - (The default value for NAMEDATALEN is 32 bytes.)

+

Normally, to checkout the head branch, you just cd to the place + you want to contain the toplevel "pgsql" directory and say

-typedef struct nameData
-    {
-        char        data[NAMEDATALEN];
-    } NameData;
-    typedef NameData *Name;
-
+    cvs ... checkout pgsql
- Table, column, type, function, and view names that come into the - backend via user queries are stored as variable-length, - null-terminated character strings. -

Many functions are called with both types of names, ie. - heap_open(). Because the Name type is null-terminated, it is - safe to pass it to a function expecting a char *. Because there are - many cases where on-disk names(Name) are compared to user-supplied - names(char *), there are many cases where Name and char * are used - interchangeably.

+

To get a past branch, you cd to whereever you want it and + say

+
+    cvs ... checkout -r BRANCHNAME pgsql
+
+ +

For example, just a couple days ago I did

+
+    mkdir ~postgres/REL7_1
+    cd ~postgres/REL7_1
+    cvs ... checkout -r REL7_1_STABLE pgsql
+
+ +

and now I have a maintenance copy of 7.1.*.

+ +

When you've done a checkout in this way, the branch name is + "sticky": CVS automatically knows that this directory tree is for + the branch, and whenever you do "cvs update" or "cvs commit" in + this tree, you'll fetch or store the latest version in the branch, + not the head version. Easy as can be.

+ +

So, if you have a patch that needs to apply to both the head and + a recent stable branch, you have to make the edits and do the + commit twice, once in your development tree and once in your stable + branch tree. This is kind of a pain, which is why we don't normally + fork the tree right away after a major release --- we wait for a + dot-release or two, so that we won't have to double-patch the first + wave of fixes.

+ +
+

Technical Questions

+
-

9) How do I efficiently access information in +

2.1) How do I efficiently access information in tables from the backend code?

You first need to find the tuples(rows) you are interested in. @@ -460,330 +628,172 @@ ReleaseBuffer(), in the heap_fetch() case. Or it may be a palloc'ed tuple, that you must pfree() when finished. -

10) What is elog()?

+

2.2) Why are table, column, type, function, view + names sometimes referenced as Name or NameData, and + sometimes as char *?

-

elog() is used to send messages to the front-end, and - optionally terminate the current query being processed. The first - parameter is an elog level of NOTICE, DEBUG, - ERROR, or FATAL. NOTICE prints on the user's - terminal and the postmaster logs. DEBUG prints only in the - postmaster logs. ERROR prints in both places, and terminates - the current query, never returning from the call. FATAL - terminates the backend process. The remaining parameters of - elog are a printf-style set of parameters to - print.

+

Table, column, type, function, and view names are stored in + system tables in columns of type Name. Name is a + fixed-length, null-terminated type of NAMEDATALEN bytes. + (The default value for NAMEDATALEN is 32 bytes.)

+
+typedef struct nameData
+    {
+        char        data[NAMEDATALEN];
+    } NameData;
+    typedef NameData *Name;
+
+
+ Table, column, type, function, and view names that come into the + backend via user queries are stored as variable-length, + null-terminated character strings. -

11) What is configure all about?

+

Many functions are called with both types of names, ie. + heap_open(). Because the Name type is null-terminated, it is + safe to pass it to a function expecting a char *. Because there are + many cases where on-disk names(Name) are compared to user-supplied + names(char *), there are many cases where Name and char * are used + interchangeably.

-

The files configure and configure.in are part of - the GNU autoconf package. Configure allows us to test for - various capabilities of the OS, and to set variables that can then - be tested in C programs and Makefiles. Autoconf is installed on the - PostgreSQL main server. To add options to configure, edit - configure.in, and then run autoconf to generate - configure.

- -

When configure is run by the user, it tests various OS - capabilities, stores those in config.status and - config.cache, and modifies a list of *.in files. For - example, if there exists a Makefile.in, configure generates - a Makefile that contains substitutions for all @var@ - parameters found by configure.

- -

When you need to edit files, make sure you don't waste time - modifying files generated by configure. Edit the *.in - file, and re-run configure to recreate the needed file. If - you run make distclean from the top-level source directory, - all files derived by configure are removed, so you see only the - file contained in the source distribution.

- -

12) How do I add a new port?

- -

There are a variety of places that need to be modified to add a - new port. First, start in the src/template directory. Add an - appropriate entry for your OS. Also, use src/config.guess to - add your OS to src/template/.similar. You shouldn't match - the OS version exactly. The configure test will look for an - exact OS version number, and if not found, find a match without - version number. Edit src/configure.in to add your new OS. - (See configure item above.) You will need to run autoconf, or patch - src/configure too.

- -

Then, check src/include/port and add your new OS file, - with appropriate values. Hopefully, there is already locking code - in src/include/storage/s_lock.h for your CPU. There is also - a src/makefiles directory for port-specific Makefile - handling. There is a backend/port directory if you need - special files for your OS.

- -

13) What is CommandCounterIncrement()?

- -

Normally, transactions can not see the rows they modify. This - allows UPDATE foo SET x = x + 1 to work correctly.

- -

However, there are cases where a transactions needs to see rows - affected in previous parts of the transaction. This is accomplished - using a Command Counter. Incrementing the counter allows - transactions to be broken into pieces so each piece can see rows - modified by previous pieces. CommandCounterIncrement() - increments the Command Counter, creating a new part of the - transaction.

- -

14) Why don't we use threads in the - backend?

- -

There are several reasons threads are not used:

- - - -

15) How are RPM's packaged?

- -

This was written by Lamar Owen:

- -

2001-05-03

- -

As to how the RPMs are built -- to answer that question sanely - requires me to know how much experience you have with the whole RPM - paradigm. 'How is the RPM built?' is a multifaceted question. The - obvious simple answer is that I maintain:

- -
    -
  1. A set of patches to make certain portions of the source tree - 'behave' in the different environment of the RPMset;
    2. +

    2.3) Why do we use Node and List to + make data structures?

    -
  2. The initscript;
    3. +

    We do this because this allows a consistent way to pass data + inside the backend in a flexible way. Every node has a + NodeTag which specifies what type of data is inside the + Node. Lists are groups of Nodes chained together as a + forward-linked list.

    -
  3. Any other ancilliary scripts and files;
    4. +

    Here are some of the List manipulation commands:

    -
  4. A README.rpm-dist document that tries to adequately document - both the differences between the RPM build and the WHY of the - differences, as well as useful RPM environment operations (like, - using syslog, upgrading, getting postmaster to start at OS boot, - etc);
    5. +
    +
    +
    lfirst(i)
    -
  5. The spec file that throws it all together. This is not a - trivial undertaking in a package of this size.
    6. -
+
return the data at list element i.
-

I then download and build on as many different canonical - distributions as I can -- currently I am able to build on Red Hat - 6.2, 7.0, and 7.1 on my personal hardware. Occasionally I receive - opportunity from certain commercial enterprises such as Great - Bridge and PostgreSQL, Inc. to build on other distributions.

+
lnext(i)
-

I test the build by installing the resulting packages and - running the regression tests. Once the build passes these tests, I - upload to the postgresql.org ftp server and make a release - announcement. I am also responsible for maintaining the RPM - download area on the ftp site.

+
return the next list element after i.
-

You'll notice I said 'canonical' distributions above. That - simply means that the machine is as stock 'out of the box' as - practical -- that is, everything (except select few programs) on - these boxen are installed by RPM; only official Red Hat released - RPMs are used (except in unusual circumstances involving software - that will not alter the build -- for example, installing a newer - non-RedHat version of the Dia diagramming package is OK -- - installing Python 2.1 on the box that has Python 1.5.2 installed is - not, as that alters the PostgreSQL build). The RPM as uploaded is - built to as close to out-of-the-box pristine as is possible. Only - the standard released 'official to that release' compiler is used - -- and only the standard official kernel is used as well.

+
foreach(i, list)
-

For a time I built on Mandrake for RedHat consumption -- no - more. Nonstandard RPM building systems are worse than useless. - Which is not to say that Mandrake is useless! By no means is - Mandrake useless -- unless you are building Red Hat RPMs -- and Red - Hat is useless if you're trying to build Mandrake or SuSE RPMs, for - that matter. But I would be foolish to use 'Lamar Owen's Super - Special RPM Blend Distro 0.1.2' to build for public consumption! - :-)

+
+ loop through list, assigning each list element to + i. It is important to note that i is a List *, + not the data in the List element. You need to use + lfirst(i) to get at the data. Here is a typical code + snipped that loops through a List containing Var *'s + and processes each one: +
+List *i, *list;
+    
+    foreach(i, list)
+    {
+        Var *var = lfirst(i);
 
-    
I _do_ attempt to make the _source_ RPM compatible with as many
-    distributions as possible -- however, since I have limited
-    resources (as a volunteer RPM maintainer) I am limited as to the
-    amount of testing said build will get on other distributions,
-    architectures, or systems.

+        /* process var here */
+    }
+
+
+
-

And, while I understand people's desire to immediately upgrade - to the newest version, realize that I do this as a side interest -- - I have a regular, full-time job as a broadcast - engineer/webmaster/sysadmin/Technical Director which occasionally - prevents me from making timely RPM releases. This happened during - the early part of the 7.1 beta cycle -- but I believe I was pretty - much on the ball for the Release Candidates and the final - release.

+
lcons(node, list)
-

I am working towards a more open RPM distribution -- I would - dearly love to more fully document the process and put everything - into CVS -- once I figure out how I want to represent things such - as the spec file in a CVS form. It makes no sense to maintain a - changelog, for instance, in the spec file in CVS when CVS does a - better job of changelogs -- I will need to write a tool to generate - a real spec file from a CVS spec-source file that would add version - numbers, changelog entries, etc to the result before building the - RPM. IOW, I need to rethink the process -- and then go through the - motions of putting my long RPM history into CVS one version at a - time so that version history information isn't lost.

+
add node to the front of list, or create a + new list with node if list is NIL.
-

As to why all these files aren't part of the source tree, well, - unless there was a large cry for it to happen, I don't believe it - should. PostgreSQL is very platform-agnostic -- and I like that. - Including the RPM stuff as part of the Official Tarball (TM) would, - IMHO, slant that agnostic stance in a negative way. But maybe I'm - too sensitive to that. I'm not opposed to doing that if that is the - consensus of the core group -- and that would be a sneaky way to - get the stuff into CVS :-). But if the core group isn't thrilled - with the idea (and my instinct says they're not likely to be), I am - opposed to the idea -- not to keep the stuff to myself, but to not - hinder the platform-neutral stance. IMHO, of course.

+
lappend(list, node)
-

Of course, there are many projects that DO include all the files - necessary to build RPMs from their Official Tarball (TM).

+
add node to the end of list. This is more + expensive that lcons.
-

16) How are CVS branches managed?

+
nconc(list1, list2)
-

This was written by Tom Lane:

+
Concat list2 on to the end of list1.
-

2001-05-07

+
length(list)
-

If you just do basic "cvs checkout", "cvs update", "cvs commit", - then you'll always be dealing with the HEAD version of the files in - CVS. That's what you want for development, but if you need to patch - past stable releases then you have to be able to access and update - the "branch" portions of our CVS repository. We normally fork off a - branch for a stable release just before starting the development - cycle for the next release.

+
return the length of the list.
-

The first thing you have to know is the branch name for the - branch you are interested in getting at. To do this, look at some - long-lived file, say the top-level HISTORY file, with "cvs status - -v" to see what the branch names are. (Thanks to Ian Lance Taylor - for pointing out that this is the easiest way to do it.) Typical - branch names are:

-
-    REL7_1_STABLE
-    REL7_0_PATCHES
-    REL6_5_PATCHES
-
+
nth(i, list)
-

OK, so how do you do work on a branch? By far the best way is to - create a separate checkout tree for the branch and do your work in - that. Not only is that the easiest way to deal with CVS, but you - really need to have the whole past tree available anyway to test - your work. (And you *better* test your work. Never forget that - dot-releases tend to go out with very little beta testing --- so - whenever you commit an update to a stable branch, you'd better be - doubly sure that it's correct.)

+
return the i'th element in list.
-

Normally, to checkout the head branch, you just cd to the place - you want to contain the toplevel "pgsql" directory and say

-
-    cvs ... checkout pgsql
-
+
lconsi, ...
-

To get a past branch, you cd to whereever you want it and - say

+
There are integer versions of these: lconsi, lappendi, + nthi. List's containing integers instead of Node + pointers are used to hold list of relation object id's and + other integer quantities.
+ + + You can print nodes easily inside gdb. First, to disable + output truncation when you use the gdb print command: 
-    cvs ... checkout -r BRANCHNAME pgsql
+(gdb) set print elements 0
+
- -

For example, just a couple days ago I did

+ Instead of printing values in gdb format, you can use the next two + commands to print out List, Node, and structure contents in a + verbose format that is easier to understand. List's are unrolled + into nodes, and nodes are printed in detail. The first prints in a + short format, and the second in a long format: 
-    mkdir ~postgres/REL7_1
-    cd ~postgres/REL7_1
-    cvs ... checkout -r REL7_1_STABLE pgsql
+(gdb) call print(any_pointer)
+    (gdb) call pprint(any_pointer)
+
+ The output appears in the postmaster log file, or on your screen if + you are running a backend directly without a postmaster. -

and now I have a maintenance copy of 7.1.*.

- -

When you've done a checkout in this way, the branch name is - "sticky": CVS automatically knows that this directory tree is for - the branch, and whenever you do "cvs update" or "cvs commit" in - this tree, you'll fetch or store the latest version in the branch, - not the head version. Easy as can be.

- -

So, if you have a patch that needs to apply to both the head and - a recent stable branch, you have to make the edits and do the - commit twice, once in your development tree and once in your stable - branch tree. This is kind of a pain, which is why we don't normally - fork the tree right away after a major release --- we wait for a - dot-release or two, so that we won't have to double-patch the first - wave of fixes.

- -

17) How go I get involved in PostgreSQL - development?

- -

This was written by Lamar Owen:

- -

2001-06-22

- - What open source development process is used by the PostgreSQL - team? - -

Read HACKERS for six months (or a full release cycle, whichever - is longer). Really. HACKERS _is_the process. The process is not - well documented (AFAIK -- it may be somewhere that I am not aware - of) -- and it changes continually.

+

2.4) I just added a field to a structure. What + else should I do?

- What development environment (OS, system, compilers, etc) is - required to develop code? +

The structures passing around from the parser, rewrite, + optimizer, and executor require quite a bit of support. Most + structures have support routines in src/backend/nodes used + to create, copy, read, and output those structures. Make sure you + add support for your new field to these files. Find any other + places the structure may need code for your new field. mkid + is helpful with this (see above).

-

Developers Corner on the - website has links to this information. The distribution tarball - itself includes all the extra tools and documents that go beyond a - good Unix-like development environment. In general, a modern unix - with a modern gcc, GNU make or equivalent, autoconf (of a - particular version), and good working knowledge of those tools are - required.

+

2.5) Why do we use palloc() and + pfree() to allocate memory?

- What areas need support? +

palloc() and pfree() are used in place of malloc() + and free() because we automatically free all memory allocated when + a transaction completes. This makes it easier to make sure we free + memory that gets allocated in one place, but only freed much later. + There are several contexts that memory can be allocated in, and + this controls when the allocated memory is automatically freed by + the backend.

-

The TODO list.

+

2.6) What is elog()?

-

You've made the first step, by finding and subscribing to - HACKERS. Once you find an area to look at in the TODO, and have - read the documentation on the internals, etc, then you check out a - current CVS,write what you are going to write (keeping your CVS - checkout up to date in the process), and make up a patch (as a - context diff only) and send to the PATCHES list, prefereably.

+

elog() is used to send messages to the front-end, and + optionally terminate the current query being processed. The first + parameter is an elog level of NOTICE, DEBUG, + ERROR, or FATAL. NOTICE prints on the user's + terminal and the postmaster logs. DEBUG prints only in the + postmaster logs. ERROR prints in both places, and terminates + the current query, never returning from the call. FATAL + terminates the backend process. The remaining parameters of + elog are a printf-style set of parameters to + print.

-

Discussion on the patch typically happens here. If the patch - adds a major feature, it would be a good idea to talk about it - first on the HACKERS list, in order to increase the chances of it - being accepted, as well as toavoid duplication of effort. Note that - experienced developers with a proven track record usually get the - big jobs -- for more than one reason. Also note that PostgreSQL is - highly portable -- nonportable code will likely be dismissed out of - hand.

+

2.7) What is CommandCounterIncrement()?

-

Once your contributions get accepted, things move from there. - Typically, you would be added as a developer on the list on the - website when one of the other developers recommends it. Membership - on the steering committee is by invitation only, by the other - steering committee members, from what I have gathered watching - froma distance.

+

Normally, transactions can not see the rows they modify. This + allows UPDATE foo SET x = x + 1 to work correctly.

-

I make these statements from having watched the process for over - two years.

+

However, there are cases where a transactions needs to see rows + affected in previous parts of the transaction. This is accomplished + using a Command Counter. Incrementing the counter allows + transactions to be broken into pieces so each piece can see rows + modified by previous pieces. CommandCounterIncrement() + increments the Command Counter, creating a new part of the + transaction.

-

To see a good example of how one goes about this, search the - archives for the name 'Tom Lane' and see what his first post - consisted of, and where he took things. In particular, note that - this hasn't been _that_ long ago -- and his bugfixing and general - deep knowledge with this codebase is legendary. Take a few days to - read after him. And pay special attention to both the sheer - quantity as well as the painstaking quality of his work. Both are - in high demand.

- -- 2.49.0