The query is then identified as a <I>Utility</I> function or a more
complex query. A <I>Utility</I> query is processed by a
query-specific function in <A HREF="../../backend/commands">
-commands.</A> A complex query, like <B>SELECT, UPDATE,</B> and
-<B>DELETE</B> requires much more handling.
+commands.</A> A complex query, like <CODE>SELECT, UPDATE,</CODE> and
+<CODE>DELETE</CODE> requires much more handling.
<P>
The parser takes a complex query, and creates a
<A HREF="../../include/nodes/parsenodes.h">Query</A> structure that
contains all the elements used by complex queries. Query.qual holds the
-<B>WHERE</B> clause qualification, which is filled in by
+<CODE>WHERE</CODE> clause qualification, which is filled in by
<A HREF="../../backend/parser/parse_clause.c">transformWhereClause().</A>
Each table referenced in the query is represented by a <A
HREF="../../include/nodes/parsenodes.h"> RangeTableEntry,</A> and they
generated by <A HREF="../../backend/parser/parse_clause.c">
makeRangeTable().</A> Query.rtable holds the queries range table.
<P>
-Certain queries, like <B>SELECT,</B> return columns of data. Other
-queries, like <B>INSERT</B> and <B>UPDATE,</B> specify the columns
+Certain queries, like <CODE>SELECT,</CODE> return columns of data. Other
+queries, like <CODE>INSERT</CODE> and <CODE>UPDATE,</CODE> specify the columns
modified by the query. These column references are converted to <A
HREF="../../include/nodes/primnodes.h">Resdom</A> entries, which are
linked together to make up the <I>target list</I> of the query. The
target list is stored in Query.targetList, which is generated by
<A HREF="../../backend/parser/parse_target.c">transformTargetList().</A>
<P>
-Other query elements, like aggregates(<B>SUM()</B>), <B>GROUP BY,</B>
-<B>ORDER BY</B> are also stored in their own Query fields.
+Other query elements, like aggregates(<CODE>SUM()</CODE>), <CODE>GROUP BY,</CODE>
+<CODE>ORDER BY</CODE> are also stored in their own Query fields.
<P>
-The next step is for the Query to be modified by any <B>VIEWS</B> or
-<
B>RULES</B> that may apply to the query. This is performed by the <A
+The next step is for the Query to be modified by any <CODE>VIEWS</CODE> or
+<
CODE>RULES</CODE> that may apply to the query. This is performed by the <A
HREF="../../backend/rewrite">rewrite</A> system.
<P>
The <A HREF="../../backend/optimizer">optimizer</A> takes the Query
operations to be performed to execute the query. The <A
HREF="../../backend/optimizer/path">path</A> module determines the best
table join order and join type of each table in the RangeTable, using
-Query.qual(<B>WHERE</B> clause) to consider optimal index usage.
+Query.qual(<CODE>WHERE</CODE> clause) to consider optimal index usage.
<P>
The Plan is then passed to the <A
HREF="../../backend/executor">executor</A> for execution, and the result
<LI>Shared Buf Lookup Table - lookup of buffer cache block address using
table name and block number(<A HREF="../../include/storage/buf_internals.h">
BufferTag</A>)
-<LI><A HREF="../../include/storage/lock.h">LockTable (ctl)</A> - lock table
-structure, specifiying table, lock types, and backends holding or
-waiting on lock
-<LI>LockTable (lock hash) - lookup of LockTable structures using relation,
-database object ids
-<LI>LockTable (xid hash) - lookup of LockTable structures using
-transaction id, LockTable address
+<LI>MultiLevelLockTable (ctl) - <A
+HREF="../../include/storage/lock.h">LOCKCTL</A> control structure for
+each locking method. Currently, only multi-level locking is used.
+<LI>MultiLevelLockTable (lock hash) - the <A
+HREF="../../include/storage/lock.h">LOCK</A> structure, looked up using
+relation, database object ids(<A
+HREF="../../include/storage/lock.h">LOCKTAG)</A>. The lock table structure contains the
+lock modes(read, write) and circular linked list of backends (<A
+HREF="../../include/storage/proc.h">PROC</A> structure pointers) waiting
+on the lock.
+<LI>MultiLevelLockTable (xid hash) - lookup of LOCK structure address
+using transaction id, LOCK address. It is used to quickly check if the
+current transaction already has any locks on a table, rather than having
+to search through all the held locks. It also stores the modes
+(read/write) of the locks held by the current transaction. The returned
+<A HREF="../../include/storage/lock.h">XIDLookupEnt</A> structure also
+contains a pointer to the backend's PROC.lockQueue.
<LI><A HREF="../../include/storage/proc.h">Proc Header</A> - information
-about each backend, including locks held/waiting, indexed by process id
+about each backend, including locks held/waiting, indexed by process id
</UL>
Each data structure is created by calling <A
HREF="../../backend/storage/ipc/shmem.c">ShmemInitStruct(),</A> and
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