4 Current maintainer: Bruce Momjian (pgman@candle.pha.pa.us)
5 Last updated: Thu Sep 22 17:50:57 EDT 2005
7 The most recent version of this document can be viewed at
8 http://www.postgresql.org/docs/faqs.TODO.html.
10 #A hyphen, "-", marks changes that will appear in the upcoming 8.1 release.#
11 #A percent sign, "%", marks items that are easier to implement.#
13 Bracketed items, "[]", have more detail.
15 This list contains all known PostgreSQL bugs and feature requests. If
16 you would like to work on an item, please read the Developer's FAQ
23 * %Remove behavior of postmaster -o after making postmaster/postgres
25 * %Allow pooled connections to list all prepared queries
27 This would allow an application inheriting a pooled connection to know
28 the queries prepared in the current session.
30 * Allow major upgrades without dump/reload, perhaps using pg_upgrade
32 * Check for unreferenced table files created by transactions that were
33 in-progress when the server terminated abruptly
34 * Allow administrators to safely terminate individual sessions either
35 via an SQL function or SIGTERM
37 Lock table corruption following SIGTERM of an individual backend
38 has been reported in 8.0. A possible cause was fixed in 8.1, but
39 it is unknown whether other problems exist. This item mostly
40 requires additional testing rather than of writing any new code.
42 * %Set proper permissions on non-system schemas during db creation
44 Currently all schemas are owned by the super-user because they are
45 copied from the template1 database.
47 * Support table partitioning that allows a single table to be stored
48 in subtables that are partitioned based on the primary key or a WHERE
52 * Improve replication solutions
56 You can use any of the master/slave replication servers to use a
57 standby server for data warehousing. To allow read/write queries to
58 multiple servers, you need multi-master replication like pgcluster.
60 o Allow replication over unreliable or non-persistent links
65 o %Add "include file" functionality in postgresql.conf
66 o %Allow commenting of variables in postgresql.conf to restore them
69 Currently, if a variable is commented out, it keeps the
70 previous uncommented value until a server restarted.
72 o %Allow pg_hba.conf settings to be controlled via SQL
74 This would add a function to load the SQL table from
75 pg_hba.conf, and one to writes its contents to the flat file.
76 The table should have a line number that is a float so rows
77 can be inserted between existing rows, e.g. row 2.5 goes
78 between row 2 and row 3.
80 o %Allow postgresql.conf file values to be changed via an SQL
81 API, perhaps using SET GLOBAL
82 o Allow the server to be stopped/restarted via an SQL API
83 o Issue a warning if a change-on-restart-only postgresql.conf value
84 is modified and the server config files are reloaded
85 o Mark change-on-restart-only values in postgresql.conf
90 * Allow a database in tablespace t1 with tables created in
91 tablespace t2 to be used as a template for a new database created
92 with default tablespace t2
94 All objects in the default database tablespace must have default
95 tablespace specifications. This is because new databases are
96 created by copying directories. If you mix default tablespace
97 tables and tablespace-specified tables in the same directory,
98 creating a new database from such a mixed directory would create a
99 new database with tables that had incorrect explicit tablespaces.
100 To fix this would require modifying pg_class in the newly copied
101 database, which we don't currently do.
103 * Allow reporting of which objects are in which tablespaces
105 This item is difficult because a tablespace can contain objects
106 from multiple databases. There is a server-side function that
107 returns the databases which use a specific tablespace, so this
108 requires a tool that will call that function and connect to each
109 database to find the objects in each database for that tablespace.
111 o %Add a GUC variable to control the tablespace for temporary objects
114 It could start with a random tablespace from a supplied list and
115 cycle through the list.
117 o Allow WAL replay of CREATE TABLESPACE to work when the directory
118 structure on the recovery computer is different from the original
120 o Allow per-tablespace quotas
123 * Point-In-Time Recovery (PITR)
125 o Allow point-in-time recovery to archive partially filled
126 write-ahead logs [pitr]
128 Currently only full WAL files are archived. This means that the
129 most recent transactions aren't available for recovery in case
130 of a disk failure. This could be triggered by a user command or
133 o Automatically force archiving of partially-filled WAL files when
134 pg_stop_backup() is called or the server is stopped
136 Doing this will allow administrators to know more easily when
137 the archive contins all the files needed for point-in-time
140 o %Create dump tool for write-ahead logs for use in determining
141 transaction id for point-in-time recovery
142 o Allow a warm standby system to also allow read-only queries
145 This is useful for checking PITR recovery.
147 o Allow the PITR process to be debugged and data examined
153 * Allow server log information to be output as INSERT statements
155 This would allow server log information to be easily loaded into
156 a database for analysis.
158 * %Add ability to monitor the use of temporary sort files
159 * Allow server logs to be remotely read and removed using SQL commands
165 * Improve the MONEY data type
167 Change the MONEY data type to use DECIMAL internally, with special
168 locale-aware output formatting.
170 * Change NUMERIC to enforce the maximum precision, and increase it
171 * Add NUMERIC division operator that doesn't round?
173 Currently NUMERIC _rounds_ the result to the specified precision.
174 This means division can return a result that multiplied by the
175 divisor is greater than the dividend, e.g. this returns a value > 10:
177 SELECT (10::numeric(2,0) / 6::numeric(2,0))::numeric(2,0) * 6;
179 The positive modulus result returned by NUMERICs might be considered
180 inaccurate, in one sense.
182 * Have sequence dependency track use of DEFAULT sequences,
184 * %Disallow changing default expression of a SERIAL column?
185 * Fix data types where equality comparison isn't intuitive, e.g. box
186 * %Prevent INET cast to CIDR if the unmasked bits are not zero, or
188 * %Prevent INET cast to CIDR from droping netmask, SELECT '1.1.1.1'::inet::cidr
189 * Allow INET + INT4 to increment the host part of the address, or
190 throw an error on overflow
191 * %Add 'tid != tid ' operator for use in corruption recovery
192 * Allow user-defined types to specify a type modifier at table creation
198 o Allow infinite dates just like infinite timestamps
199 o Add a GUC variable to allow output of interval values in ISO8601
201 o Merge hardwired timezone names with the TZ database; allow either
202 kind everywhere a TZ name is currently taken
203 o Allow customization of the known set of TZ names (generalize the
204 present australian_timezones hack)
205 o Allow TIMESTAMP WITH TIME ZONE to store the original timezone
206 information, either zone name or offset from UTC [timezone]
208 If the TIMESTAMP value is stored with a time zone name, interval
209 computations should adjust based on the time zone rules.
211 o Fix SELECT '0.01 years'::interval, '0.01 months'::interval
212 o Fix SELECT INTERVAL '1' MONTH
213 o Add ISO INTERVAL handling
214 o Add support for day-time syntax, INTERVAL '1 2:03:04' DAY TO
216 o Add support for year-month syntax, INTERVAL '50-6' YEAR TO MONTH
217 o For syntax that isn't uniquely ISO or PG syntax, like '1:30' or
218 '1', treat as ISO if there is a range specification clause,
219 and as PG if there no clause is present, e.g. interpret
220 '1:30' MINUTE TO SECOND as '1 minute 30 seconds', and
221 interpret '1:30' as '1 hour, 30 minutes'
222 o Interpret INTERVAL '1 year' MONTH as CAST (INTERVAL '1 year' AS
223 INTERVAL MONTH), and this should return '12 months'
224 o Round or truncate values to the requested precision, e.g.
225 INTERVAL '11 months' AS YEAR should return one or zero
226 o Support precision, CREATE TABLE foo (a INTERVAL MONTH(3))
231 o Allow NULLs in arrays
232 o Delay resolution of array expression's data type so assignment
233 coercion can be performed on empty array expressions
238 o Improve vacuum of large objects, like /contrib/vacuumlo?
239 o Add security checking for large objects
240 o Auto-delete large objects when referencing row is deleted
242 /contrib/lo offers this functionality.
244 o Allow read/write into TOAST values like large objects
246 This requires the TOAST column to be stored EXTERNAL.
252 * Allow INET subnet tests using non-constants to be indexed
253 * Add transaction_timestamp(), statement_timestamp(), clock_timestamp()
256 Current CURRENT_TIMESTAMP returns the start time of the current
257 transaction, and gettimeofday() returns the wallclock time. This will
258 make time reporting more consistent and will allow reporting of
259 the statement start time.
261 * %Add pg_get_acldef(), pg_get_typedefault(), and pg_get_attrdef()
262 * Allow to_char() to print localized month names
263 * Allow functions to have a schema search path specified at creation time
264 * Allow substring/replace() to get/set bit values
265 * Allow to_char() on interval values to accumulate the highest unit
268 Some special format flag would be required to request such
269 accumulation. Such functionality could also be added to EXTRACT.
270 Prevent accumulation that crosses the month/day boundary because of
271 the uneven number of days in a month.
273 o to_char(INTERVAL '1 hour 5 minutes', 'MI') => 65
274 o to_char(INTERVAL '43 hours 20 minutes', 'MI' ) => 2600
275 o to_char(INTERVAL '43 hours 20 minutes', 'WK:DD:HR:MI') => 0:1:19:20
276 o to_char(INTERVAL '3 years 5 months','MM') => 41
278 * Add sleep() function, remove from regress.c
281 Multi-Language Support
282 ======================
284 * Add NCHAR (as distinguished from ordinary varchar),
285 * Allow locale to be set at database creation
287 Currently locale can only be set during initdb. No global tables have
288 locale-aware columns. However, the database template used during
289 database creation might have locale-aware indexes. The indexes would
290 need to be reindexed to match the new locale.
292 * Allow encoding on a per-column basis
294 Right now only one encoding is allowed per database.
296 * Support multiple simultaneous character sets, per SQL92
297 * Improve UTF8 combined character handling?
298 * Add octet_length_server() and octet_length_client()
299 * Make octet_length_client() the same as octet_length()?
300 * Fix problems with wrong runtime encoding conversion for NLS message files
306 * %Automatically create rules on views so they are updateable, per SQL99
308 We can only auto-create rules for simple views. For more complex
309 cases users will still have to write rules.
311 * Add the functionality for WITH CHECK OPTION clause of CREATE VIEW
312 * Allow NOTIFY in rules involving conditionals
313 * Allow VIEW/RULE recompilation when the underlying tables change
315 Another issue is whether underlying table changes should be reflected
316 in the view, e.g. should SELECT * show additional columns if they
317 are added after the view is created.
323 * Change LIMIT/OFFSET and FETCH/MOVE to use int8
324 * Add CORRESPONDING BY to UNION/INTERSECT/EXCEPT
325 * Add ROLLUP, CUBE, GROUPING SETS options to GROUP BY
326 * %Allow SET CONSTRAINTS to be qualified by schema/table name
327 * %Allow TRUNCATE ... CASCADE/RESTRICT
329 This is like DELETE CASCADE, but truncates.
331 * %Add a separate TRUNCATE permission
333 Currently only the owner can TRUNCATE a table because triggers are not
334 called, and the table is locked in exclusive mode.
336 * Allow PREPARE of cursors
337 * Allow PREPARE to automatically determine parameter types based on the SQL
339 * Allow finer control over the caching of prepared query plans
341 Currently, queries prepared via the libpq API are planned on first
342 execute using the supplied parameters --- allow SQL PREPARE to do the
343 same. Also, allow control over replanning prepared queries either
344 manually or automatically when statistics for execute parameters
345 differ dramatically from those used during planning.
347 * Allow LISTEN/NOTIFY to store info in memory rather than tables?
349 Currently LISTEN/NOTIFY information is stored in pg_listener. Storing
350 such information in memory would improve performance.
352 * Add optional textual message to NOTIFY
354 This would allow an informational message to be added to the notify
355 message, perhaps indicating the row modified or other custom
358 * Add a GUC variable to warn about non-standard SQL usage in queries
359 * Add MERGE command that does UPDATE/DELETE, or on failure, INSERT (rules,
361 * Add NOVICE output level for helpful messages like automatic sequence/index
363 * %Add COMMENT ON for all cluster global objects (roles, databases
365 * %Make row-wise comparisons work per SQL spec
366 * Add RESET CONNECTION command to reset all session state
368 This would include resetting of all variables (RESET ALL), dropping of
369 temporary tables, removing any NOTIFYs, cursors, open transactions,
370 prepared queries, currval()s, etc. This could be used for connection
371 pooling. We could also change RESET ALL to have this functionality.
372 The difficult of this features is allowing RESET ALL to not affect
373 changes made by the interface driver for its internal use. One idea
374 is for this to be a protocol-only feature. Another approach is to
375 notify the protocol when a RESET CONNECTION command is used.
377 * Add GUC to issue notice about queries that use unjoined tables
378 * Allow EXPLAIN to identify tables that were skipped because of
380 * Allow EXPLAIN output to be more easily processed by scripts
381 * Eventually enable escape_string_warning and standard_conforming_strings
386 o Allow CREATE TABLE AS to determine column lengths for complex
387 expressions like SELECT col1 || col2
388 o Use more reliable method for CREATE DATABASE to get a consistent
390 o Add ON COMMIT capability to CREATE TABLE AS ... SELECT
394 o Allow UPDATE to handle complex aggregates [update]?
395 o Allow an alias to be provided for the target table in
398 This is not SQL-spec but many DBMSs allow it.
400 o Allow UPDATE tab SET ROW (col, ...) = (...) for updating multiple
406 o %Have ALTER TABLE RENAME rename SERIAL sequence names
407 o Add ALTER DOMAIN to modify the underlying data type
408 o %Allow ALTER TABLE ... ALTER CONSTRAINT ... RENAME
409 o %Allow ALTER TABLE to change constraint deferrability and actions
410 o Add missing object types for ALTER ... SET SCHEMA
411 o Allow ALTER TABLESPACE to move to different directories
412 o Allow databases to be moved to different tablespaces
413 o Allow moving system tables to other tablespaces, where possible
415 Currently non-global system tables must be in the default database
416 tablespace. Global system tables can never be moved.
418 o %Disallow dropping of an inherited constraint
419 o %Prevent child tables from altering or dropping constraints
420 like CHECK that were inherited from the parent table
425 o Automatically maintain clustering on a table
427 This might require some background daemon to maintain clustering
428 during periods of low usage. It might also require tables to be only
429 paritally filled for easier reorganization. Another idea would
430 be to create a merged heap/index data file so an index lookup would
431 automatically access the heap data too. A third idea would be to
432 store heap rows in hashed groups, perhaps using a user-supplied
435 o %Add default clustering to system tables
437 To do this, determine the ideal cluster index for each system
438 table and set the cluster setting during initdb.
443 o Allow COPY to report error lines and continue
445 This requires the use of a savepoint before each COPY line is
446 processed, with ROLLBACK on COPY failure.
448 o %Have COPY return the number of rows loaded/unloaded?
449 o Allow COPY on a newly-created table to skip WAL logging
451 On crash recovery, the table involved in the COPY would
452 be removed or have its heap and index files truncated. One
453 issue is that no other backend should be able to add to
454 the table at the same time, which is something that is
457 o Allow COPY to output from views
459 Another idea would be to allow actual SELECT queries in a COPY.
464 o Allow column-level privileges
465 o %Allow GRANT/REVOKE permissions to be applied to all schema objects
468 The proposed syntax is:
469 GRANT SELECT ON ALL TABLES IN public TO phpuser;
470 GRANT SELECT ON NEW TABLES IN public TO phpuser;
472 * Allow GRANT/REVOKE permissions to be inherited by objects based on
478 o Allow UPDATE/DELETE WHERE CURRENT OF cursor
480 This requires using the row ctid to map cursor rows back to the
481 original heap row. This become more complicated if WITH HOLD cursors
482 are to be supported because WITH HOLD cursors have a copy of the row
483 and no FOR UPDATE lock.
485 o Prevent DROP TABLE from dropping a row referenced by its own open
488 o %Allow pooled connections to list all open WITH HOLD cursors
490 Because WITH HOLD cursors exist outside transactions, this allows
491 them to be listed so they can be closed.
496 o Allow INSERT/UPDATE of the system-generated oid value for a row
497 o Allow INSERT INTO tab (col1, ..) VALUES (val1, ..), (val2, ..)
498 o Allow INSERT/UPDATE ... RETURNING new.col or old.col
500 This is useful for returning the auto-generated key for an INSERT.
501 One complication is how to handle rules that run as part of
507 o Add SET PERFORMANCE_TIPS option to suggest INDEX, VACUUM, VACUUM
509 o Add SET PATH for schemas?
511 This is basically the same as SET search_path.
514 * Server-Side Languages
516 o Fix PL/pgSQL RENAME to work on variables other than OLD/NEW
517 o Allow function parameters to be passed by name,
518 get_employee_salary(emp_id => 12345, tax_year => 2001)
519 o Add Oracle-style packages
520 o Add table function support to pltcl, plpython
521 o Add capability to create and call PROCEDURES
522 o Allow PL/pgSQL to handle %TYPE arrays, e.g. tab.col%TYPE[]
523 o Allow function argument names to be queries from PL/PgSQL
524 o Add MOVE to PL/pgSQL
525 o Add support for polymorphic arguments and return types to
526 languages other than PL/PgSQL
527 o Add support for OUT and INOUT parameters to languages other
529 o Add single-step debugging of PL/PgSQL functions
535 * Add a libpq function to support Parse/DescribeStatement capability
536 * Prevent libpq's PQfnumber() from lowercasing the column name?
537 * Add PQescapeIdentifier() to libpq
538 * Have initdb set the input DateStyle (MDY or DMY) based on locale?
539 * Have pg_ctl look at PGHOST in case it is a socket directory?
540 * Allow pg_ctl to work properly with configuration files located outside
543 pg_ctl can not read the pid file because it isn't located in the
544 config directory but in the PGDATA directory. The solution is to
545 allow pg_ctl to read and understand postgresql.conf to find the
546 data_directory value.
551 o Have psql show current values for a sequence
552 o Move psql backslash database information into the backend, use
553 mnemonic commands? [psql]
555 This would allow non-psql clients to pull the same information out
556 of the database as psql.
558 o Fix psql's display of schema information (Neil)
559 o Allow psql \pset boolean variables to set to fixed values, rather
561 o Consistently display privilege information for all objects in psql
562 o Improve psql's handling of multi-line queries
564 Currently, while \e saves a single query as one entry, interactive
565 queries are saved one line at a time. Ideally all queries
566 whould be saved like \e does.
568 o Allow multi-line column values to align in the proper columns
570 If the second output column value is 'a\nb', the 'b' should appear
571 in the second display column, rather than the first column as it
577 o %Have pg_dump use multi-statement transactions for INSERT dumps
578 o %Allow pg_dump to use multiple -t and -n switches [pg_dump]
579 o %Add dumping of comments on composite type columns
580 o %Add dumping of comments on index columns
581 o %Replace crude DELETE FROM method of pg_dumpall --clean for
582 cleaning of roles with separate DROP commands
583 o Stop dumping CASCADE on DROP TYPE commands in clean mode
584 o %Add full object name to the tag field. eg. for operators we need
585 '=(integer, integer)', instead of just '='.
586 o Add pg_dumpall custom format dumps?
587 o %Add CSV output format
588 o Update pg_dump and psql to use the new COPY libpq API (Christopher)
589 o Remove unnecessary function pointer abstractions in pg_dump source
597 Document differences between ecpg and the SQL standard and
598 information about the Informix-compatibility module.
600 o Solve cardinality > 1 for input descriptors / variables?
601 o Add a semantic check level, e.g. check if a table really exists
602 o fix handling of DB attributes that are arrays
603 o Use backend PREPARE/EXECUTE facility for ecpg where possible
605 o Fix nested C comments
606 o %sqlwarn[6] should be 'W' if the PRECISION or SCALE value specified
607 o Make SET CONNECTION thread-aware, non-standard?
608 o Allow multidimensional arrays
609 o Add internationalized message strings
612 Referential Integrity
613 =====================
615 * Add MATCH PARTIAL referential integrity
616 * Add deferred trigger queue file
618 Right now all deferred trigger information is stored in backend
619 memory. This could exhaust memory for very large trigger queues.
620 This item involves dumping large queues into files.
622 * Change foreign key constraint for array -> element to mean element
624 * Allow DEFERRABLE UNIQUE constraints?
625 * Allow triggers to be disabled in only the current session.
627 This is currently possible by starting a multi-statement transaction,
628 modifying the system tables, performing the desired SQL, restoring the
629 system tables, and committing the transaction. ALTER TABLE ...
630 TRIGGER requires a table lock so it is not ideal for this usage.
632 * With disabled triggers, allow pg_dump to use ALTER TABLE ADD FOREIGN KEY
634 If the dump is known to be valid, allow foreign keys to be added
635 without revalidating the data.
637 * Allow statement-level triggers to access modified rows
638 * Support triggers on columns (Greg Sabino Mullane)
639 * Enforce referential integrity for system tables
640 * Allow AFTER triggers on system tables
642 System tables are modified in many places in the backend without going
643 through the executor and therefore not causing triggers to fire. To
644 complete this item, the functions that modify system tables will have
651 * Flush cached query plans when the dependent objects change
652 * Track dependencies in function bodies and recompile/invalidate
654 This is particularly important for references to temporary tables
655 in PL/PgSQL because PL/PgSQL caches query plans. The only workaround
656 in PL/PgSQL is to use EXECUTE. One complexity is that a function
657 might itself drop and recreate dependent tables, causing it to
658 invalidate its own query plan.
664 * Add SQL99 WITH clause to SELECT
665 * Add SQL99 WITH RECURSIVE to SELECT
666 * Add pre-parsing phase that converts non-ISO syntax to supported
669 This could allow SQL written for other databases to run without
672 * Allow plug-in modules to emulate features from other databases
673 * SQL*Net listener that makes PostgreSQL appear as an Oracle database
675 * Allow queries across databases or servers with transaction
678 This can be done using dblink and two-phase commit.
680 * Add the features of packages
682 o Make private objects accessable only to objects in the same schema
683 o Allow current_schema.objname to access current schema objects
684 o Add session variables
685 o Allow nested schemas
691 * Allow inherited tables to inherit index, UNIQUE constraint, and primary
693 * UNIQUE INDEX on base column not honored on INSERTs/UPDATEs from
694 inherited table: INSERT INTO inherit_table (unique_index_col) VALUES
697 The main difficulty with this item is the problem of creating an index
698 that can span more than one table.
700 * Allow SELECT ... FOR UPDATE on inherited tables
701 * Add UNIQUE capability to non-btree indexes
702 * Prevent index uniqueness checks when UPDATE does not modify the column
704 Uniqueness (index) checks are done when updating a column even if the
705 column is not modified by the UPDATE.
707 * Allow the creation of on-disk bitmap indexes which can be quickly
708 combined with other bitmap indexes
710 Such indexes could be more compact if there are only a few distinct values.
711 Such indexes can also be compressed. Keeping such indexes updated can be
714 * Allow use of indexes to search for NULLs
716 One solution is to create a partial index on an IS NULL expression.
718 * Allow accurate statistics to be collected on indexes with more than
719 one column or expression indexes, perhaps using per-index statistics
720 * Add fillfactor to control reserved free space during index creation
721 * Allow the creation of indexes with mixed ascending/descending specifiers
722 * Allow constraint_exclusion to work for UNIONs like it does for
723 inheritance, allow it to work for UPDATE and DELETE queries, and allow
724 it to be used for all queries with little performance impact
729 o Add more GIST index support for geometric data types
730 o Allow GIST indexes to create certain complex index types, like
731 digital trees (see Aoki)
735 o Pack hash index buckets onto disk pages more efficiently
737 Currently only one hash bucket can be stored on a page. Ideally
738 several hash buckets could be stored on a single page and greater
739 granularity used for the hash algorithm.
741 o Consider sorting hash buckets so entries can be found using a
742 binary search, rather than a linear scan
744 o In hash indexes, consider storing the hash value with or instead
747 o Add WAL logging for crash recovery
748 o Allow multi-column hash indexes
754 * Improve commit_delay handling to reduce fsync()
755 * Determine optimal fdatasync/fsync, O_SYNC/O_DSYNC options
757 Ideally this requires a separate test program that can be run
758 at initdb time or optionally later.
760 * %Add an option to sync() before fsync()'ing checkpoint files
761 * Add program to test if fsync has a delay compared to non-fsync
767 * Allow free-behind capability for large sequential scans, perhaps using
770 Posix_fadvise() can control both sequential/random file caching and
771 free-behind behavior, but it is unclear how the setting affects other
772 backends that also have the file open, and the feature is not supported
773 on all operating systems.
777 We could use a fixed row count and a +/- count to follow MVCC
778 visibility rules, or a single cached value could be used and
779 invalidated if anyone modifies the table. Another idea is to
780 get a count directly from a unique index, but for this to be
781 faster than a sequential scan it must avoid access to the heap
782 to obtain tuple visibility information.
784 * Allow data to be pulled directly from indexes
786 Currently indexes do not have enough tuple visibility information
787 to allow data to be pulled from the index without also accessing
788 the heap. One way to allow this is to set a bit to index tuples
789 to indicate if a tuple is currently visible to all transactions
790 when the first valid heap lookup happens. This bit would have to
791 be cleared when a heap tuple is expired.
794 * Consider automatic caching of queries at various levels:
800 * Allow sequential scans to take advantage of other concurrent
801 sequentiqal scans, also called "Synchronised Scanning"
803 One possible implementation is to start sequential scans from the lowest
804 numbered buffer in the shared cache, and when reaching the end wrap
805 around to the beginning, rather than always starting sequential scans
806 at the start of the table.
812 * Improve speed with indexes
814 For large table adjustements during VACUUM FULL, it is faster to
815 reindex rather than update the index.
817 * Reduce lock time during VACUUM FULL by moving tuples with read lock,
818 then write lock and truncate table
820 Moved tuples are invisible to other backends so they don't require a
821 write lock. However, the read lock promotion to write lock could lead
822 to deadlock situations.
824 * Auto-fill the free space map by scanning the buffer cache or by
825 checking pages written by the background writer
826 * Create a bitmap of pages that need vacuuming
828 Instead of sequentially scanning the entire table, have the background
829 writer or some other process record pages that have expired rows, then
830 VACUUM can look at just those pages rather than the entire table. In
831 the event of a system crash, the bitmap would probably be invalidated.
832 One complexity is that index entries still have to be vacuumed, and
833 doing this without an index scan (by using the heap values to find the
834 index entry) might be slow and unreliable, especially for user-defined
837 * %Add system view to show free space map contents
842 o Use free-space map information to guide refilling
843 o %Issue log message to suggest VACUUM FULL if a table is nearly
845 o Improve xid wraparound detection by recording per-table rather
852 * Add code to detect an SMP machine and handle spinlocks accordingly
853 from distributted.net, http://www1.distributed.net/source,
854 in client/common/cpucheck.cpp
856 On SMP machines, it is possible that locks might be released shortly,
857 while on non-SMP machines, the backend should sleep so the process
858 holding the lock can complete and release it.
860 * Fix priority ordering of read and write light-weight locks (Neil)
863 Startup Time Improvements
864 =========================
866 * Experiment with multi-threaded backend [thread]
868 This would prevent the overhead associated with process creation. Most
869 operating systems have trivial process creation time compared to
870 database startup overhead, but a few operating systems (WIn32,
871 Solaris) might benefit from threading. Also explore the idea of
872 a single session using multiple threads to execute a query faster.
874 * Add connection pooling
876 It is unclear if this should be done inside the backend code or done
877 by something external like pgpool. The passing of file descriptors to
878 existing backends is one of the difficulties with a backend approach.
884 * Eliminate need to write full pages to WAL before page modification [wal]
886 Currently, to protect against partial disk page writes, we write
887 full page images to WAL before they are modified so we can correct any
888 partial page writes during recovery. These pages can also be
889 eliminated from point-in-time archive files.
891 o When off, write CRC to WAL and check file system blocks
894 If CRC check fails during recovery, remember the page in case
895 a later CRC for that page properly matches.
897 o Write full pages during file system write and not when
898 the page is modified in the buffer cache
900 This allows most full page writes to happen in the background
901 writer. It might cause problems for applying WAL on recovery
902 into a partially-written page, but later the full page will be
905 * Allow WAL traffic to be streamed to another server for stand-by
907 * Reduce WAL traffic so only modified values are written rather than
909 * Allow the pg_xlog directory location to be specified during initdb
910 with a symlink back to the /data location
911 * Allow WAL information to recover corrupted pg_controldata
912 * Find a way to reduce rotational delay when repeatedly writing
915 Currently fsync of WAL requires the disk platter to perform a full
916 rotation to fsync again. One idea is to write the WAL to different
917 offsets that might reduce the rotational delay.
919 * Allow buffered WAL writes and fsync
921 Instead of guaranteeing recovery of all committed transactions, this
922 would provide improved performance by delaying WAL writes and fsync
923 so an abrupt operating system restart might lose a few seconds of
924 committed transactions but still be consistent. We could perhaps
925 remove the 'fsync' parameter (which results in an an inconsistent
926 database) in favor of this capability.
932 * Add missing optimizer selectivities for date, r-tree, etc
933 * Allow ORDER BY ... LIMIT # to select high/low value without sort or
934 index using a sequential scan for highest/lowest values
936 Right now, if no index exists, ORDER BY ... LIMIT # requires we sort
937 all values to return the high/low value. Instead The idea is to do a
938 sequential scan to find the high/low value, thus avoiding the sort.
939 MIN/MAX already does this, but not for LIMIT > 1.
941 * Precompile SQL functions to avoid overhead
942 * Create utility to compute accurate random_page_cost value
943 * Improve ability to display optimizer analysis using OPTIMIZER_DEBUG
944 * Have EXPLAIN ANALYZE highlight poor optimizer estimates
945 * Consider using hash buckets to do DISTINCT, rather than sorting
947 This would be beneficial when there are few distinct values. This is
948 already used by GROUP BY.
950 * Log queries where the optimizer row estimates were dramatically
951 different from the number of rows actually found?
954 Miscellaneous Performance
955 =========================
957 * Do async I/O for faster random read-ahead of data
959 Async I/O allows multiple I/O requests to be sent to the disk with
960 results coming back asynchronously.
962 * Use mmap() rather than SYSV shared memory or to write WAL files?
964 This would remove the requirement for SYSV SHM but would introduce
965 portability issues. Anonymous mmap (or mmap to /dev/zero) is required
966 to prevent I/O overhead.
968 * Consider mmap()'ing files into a backend?
970 Doing I/O to large tables would consume a lot of address space or
971 require frequent mapping/unmapping. Extending the file also causes
972 mapping problems that might require mapping only individual pages,
973 leading to thousands of mappings. Another problem is that there is no
974 way to _prevent_ I/O to disk from the dirty shared buffers so changes
975 could hit disk before WAL is written.
977 * Add a script to ask system configuration questions and tune postgresql.conf
978 * Merge xmin/xmax/cmin/cmax back into three header fields
980 Before subtransactions, there used to be only three fields needed to
981 store these four values. This was possible because only the current
982 transaction looks at the cmin/cmax values. If the current transaction
983 created and expired the row the fields stored where xmin (same as
984 xmax), cmin, cmax, and if the transaction was expiring a row from a
985 another transaction, the fields stored were xmin (cmin was not
986 needed), xmax, and cmax. Such a system worked because a transaction
987 could only see rows from another completed transaction. However,
988 subtransactions can see rows from outer transactions, and once the
989 subtransaction completes, the outer transaction continues, requiring
990 the storage of all four fields. With subtransactions, an outer
991 transaction can create a row, a subtransaction expire it, and when the
992 subtransaction completes, the outer transaction still has to have
993 proper visibility of the row's cmin, for example, for cursors.
995 One possible solution is to create a phantom cid which represents a
996 cmin/cmax pair and is stored in local memory. Another idea is to
997 store both cmin and cmax only in local memory.
999 * Research storing disk pages with no alignment/padding
1005 * Add use of 'const' for variables in source tree
1006 * Rename some /contrib modules from pg* to pg_*
1007 * Move some things from /contrib into main tree
1008 * Move some /contrib modules out to their own project sites
1009 * %Remove warnings created by -Wcast-align
1010 * Move platform-specific ps status display info from ps_status.c to ports
1011 * Add optional CRC checksum to heap and index pages
1012 * Improve documentation to build only interfaces (Marc)
1013 * Remove or relicense modules that are not under the BSD license, if possible
1014 * %Remove memory/file descriptor freeing before ereport(ERROR)
1015 * Acquire lock on a relation before building a relcache entry for it
1016 * %Promote debug_query_string into a server-side function current_query()
1017 * %Allow the identifier length to be increased via a configure option
1018 * Remove Win32 rename/unlink looping if unnecessary
1019 * Allow cross-compiling by generating the zic database on the target system
1020 * Improve NLS maintenace of libpgport messages linked onto applications
1021 * Allow ecpg to work with MSVC and BCC
1022 * Add xpath_array() to /contrib/xml2 to return results as an array
1023 * Allow building in directories containing spaces
1025 This is probably not possible because 'gmake' and other compiler tools
1026 do not fully support quoting of paths with spaces.
1028 * Allow installing to directories containing spaces
1030 This is possible if proper quoting is added to the makefiles for the
1031 install targets. Because PostgreSQL supports relocatable installs, it
1032 is already possible to install into a directory that doesn't contain
1033 spaces and then copy the install to a directory with spaces.
1035 * Fix sgmltools so PDFs can be generated with bookmarks
1036 * %Clean up compiler warnings (especially with gcc version 4)
1037 * Add function to return the thread safety status of libpq and ecpg
1038 * Use UTF8 encoding for NLS messages so all server encodings can
1040 * Update Bonjour to work with newer cross-platform SDK
1041 * Remove BeOS and QNX-specific code
1045 o Remove configure.in check for link failure when cause is found
1046 o Remove readdir() errno patch when runtime/mingwex/dirent.c rev
1048 o Remove psql newline patch when we find out why mingw outputs an
1050 o Allow psql to use readline once non-US code pages work with
1052 o Re-enable timezone output on log_line_prefix '%t' when a
1053 shorter timezone string is available
1054 o Fix problem with shared memory on the Win32 Terminal Server
1057 * Wire Protocol Changes
1059 o Allow dynamic character set handling
1060 o Add decoded type, length, precision
1062 o Update clients to use data types, typmod, schema.table.column names
1063 of result sets using new query protocol
1066 ---------------------------------------------------------------------------
1069 Developers who have claimed items are:
1070 --------------------------------------
1071 * Alvaro is Alvaro Herrera <alvherre@dcc.uchile.cl>
1072 * Andrew is Andrew Dunstan <andrew@dunslane.net>
1073 * Bruce is Bruce Momjian <pgman@candle.pha.pa.us> of Software Research Assoc.
1074 * Christopher is Christopher Kings-Lynne <chriskl@familyhealth.com.au> of
1075 Family Health Network
1076 * Claudio is Claudio Natoli <claudio.natoli@memetrics.com>
1077 * D'Arcy is D'Arcy J.M. Cain <darcy@druid.net> of The Cain Gang Ltd.
1078 * Fabien is Fabien Coelho <coelho@cri.ensmp.fr>
1079 * Gavin is Gavin Sherry <swm@linuxworld.com.au> of Alcove Systems Engineering
1080 * Greg is Greg Sabino Mullane <greg@turnstep.com>
1081 * Hiroshi is Hiroshi Inoue <Inoue@tpf.co.jp>
1082 * Jan is Jan Wieck <JanWieck@Yahoo.com> of Afilias, Inc.
1083 * Joe is Joe Conway <mail@joeconway.com>
1084 * Karel is Karel Zak <zakkr@zf.jcu.cz>
1085 * Magnus is Magnus Hagander <mha@sollentuna.net>
1086 * Marc is Marc Fournier <scrappy@hub.org> of PostgreSQL, Inc.
1087 * Matthew T. O'Connor <matthew@zeut.net>
1088 * Michael is Michael Meskes <meskes@postgresql.org> of Credativ
1089 * Neil is Neil Conway <neilc@samurai.com>
1090 * Oleg is Oleg Bartunov <oleg@sai.msu.su>
1091 * Peter is Peter Eisentraut <peter_e@gmx.net>
1092 * Philip is Philip Warner <pjw@rhyme.com.au> of Albatross Consulting Pty. Ltd.
1093 * Rod is Rod Taylor <pg@rbt.ca>
1094 * Simon is Simon Riggs <simon@2ndquadrant.com>
1095 * Stephan is Stephan Szabo <sszabo@megazone23.bigpanda.com>
1096 * Tatsuo is Tatsuo Ishii <t-ishii@sra.co.jp> of Software Research Assoc.
1097 * Tom is Tom Lane <tgl@sss.pgh.pa.us> of Red Hat