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Bruce Momjian 1998-07-21 04:48:31 +00:00
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@ -43,37 +43,35 @@ Click on an item to see more detail or look at the full
<HR> <HR>
<P> <P>
A query comes to the backend via data packets arriving through TCP/IP
or Unix Domain sockets. It is loaded into a string, and passed to A query comes to the backend via data packets arriving through TCP/IP or
the Unix Domain sockets. It is loaded into a string, and passed to the
<A HREF="../../backend/parser">parser,</A> where the lexical scanner, <A HREF="../../backend/parser">parser,</A> where the lexical scanner,
<A HREF="../../backend/parser/scan.l">scan.l,</A> <A HREF="../../backend/parser/scan.l">scan.l,</A> breaks the query up
breaks the query up into tokens(words). The parser into tokens(words). The parser uses <A
uses HREF="../../backend/parser/gram.y">gram.y</A> and the tokens to identify
<A HREF="../../backend/parser/gram.y">gram.y</A> and the tokens to the query type, and load the proper query-specific structure, like <A
identify the query type, and load the proper query-specific structure, HREF="../../include/nodes/parsenodes.h">CreateStmt</A> or <A
like <A HREF="../../include/nodes/parsenodes.h">CreateStmt</A> or <A HREF="../../include/nodes/parsenodes.h">SelectStmt.</A><P>
HREF="../../include/nodes/parsenodes.h">SelectStmt.</A>
<P>
The query is then identified as a <I>Utility</I> query or a more complex The query is then identified as a <I>Utility</I> query or a more complex
query. A <I>Utility</I> query is processed by a query-specific function query. A <I>Utility</I> query is processed by a query-specific function
in <A HREF="../../backend/commands"> commands.</A> A complex query, like in <A HREF="../../backend/commands"> commands.</A> A complex query, like
<I>SELECT, UPDATE,</I> and <I>SELECT, UPDATE,</I> and <I>DELETE</I> requires much more handling.<P>
<I>DELETE</I> requires much more handling.
<P>
The parser takes a complex query, and creates a The parser takes a complex query, and creates a
<A HREF="../../include/nodes/parsenodes.h">Query</A> structure that <A HREF="../../include/nodes/parsenodes.h">Query</A> structure that
contains all the elements used by complex queries. Query.qual holds the contains all the elements used by complex queries. Query.qual holds the
<I>WHERE</I> clause qualification, which is filled in by <I>WHERE</I> clause qualification, which is filled in by <A
<A HREF="../../backend/parser/parse_clause.c">transformWhereClause().</A> HREF="../../backend/parser/parse_clause.c">transformWhereClause().</A>
Each table referenced in the query is represented by a <A Each table referenced in the query is represented by a <A
HREF="../../include/nodes/parsenodes.h"> RangeTableEntry,</A> and they HREF="../../include/nodes/parsenodes.h"> RangeTableEntry,</A> and they
are linked together to form the <I>range table</I> of the query, which is are linked together to form the <I>range table</I> of the query, which
generated by <A HREF="../../backend/parser/parse_clause.c"> is generated by <A HREF="../../backend/parser/parse_clause.c">
makeRangeTable().</A> Query.rtable holds the query's range table. makeRangeTable().</A> Query.rtable holds the query's range table.<P>
<P>
Certain queries, like <I>SELECT,</I> return columns of data. Other Certain queries, like <I>SELECT,</I> return columns of data. Other
queries, like <I>INSERT</I> and <I>UPDATE,</I> specify the columns queries, like <I>INSERT</I> and <I>UPDATE,</I> specify the columns
@ -82,18 +80,18 @@ HREF="../../include/nodes/primnodes.h">Resdom</A> entries, which are
placed in <A HREF="../../include/nodes/parsenodes.h">target list placed in <A HREF="../../include/nodes/parsenodes.h">target list
entries,</I> and linked together to make up the <I>target list</I> of entries,</I> and linked together to make up the <I>target list</I> of
the query. The target list is stored in Query.targetList, which is the query. The target list is stored in Query.targetList, which is
generated by generated by <A
<A HREF="../../backend/parser/parse_target.c">transformTargetList().</A> HREF="../../backend/parser/parse_target.c">transformTargetList().</A><P>
<P>
Other query elements, like aggregates(<I>SUM()</I>), <I>GROUP BY,</I> Other query elements, like aggregates(<I>SUM()</I>), <I>GROUP BY,</I>
and <I>ORDER BY</I> are also stored in their own Query fields. and <I>ORDER BY</I> are also stored in their own Query fields.<P>
<P>
The next step is for the Query to be modified by any <I>VIEWS</I> or The next step is for the Query to be modified by any <I>VIEWS</I> or
<I>RULES</I> that may apply to the query. This is performed by the <A <I>RULES</I> that may apply to the query. This is performed by the <A
HREF="../../backend/rewrite">rewrite</A> system. HREF="../../backend/rewrite">rewrite</A> system.<P>
<P>
The <A HREF="../../backend/optimizer">optimizer</A> takes the Query The <A HREF="../../backend/optimizer">optimizer</A> takes the Query
structure and generates an optimal <A structure and generates an optimal <A
@ -101,45 +99,46 @@ HREF="../..//include/nodes/plannodes.h">Plan,</A> which contains the
operations to be performed to execute the query. The <A operations to be performed to execute the query. The <A
HREF="../../backend/optimizer/path">path</A> module determines the best HREF="../../backend/optimizer/path">path</A> module determines the best
table join order and join type of each table in the RangeTable, using table join order and join type of each table in the RangeTable, using
Query.qual(<I>WHERE</I> clause) to consider optimal index usage. Query.qual(<I>WHERE</I> clause) to consider optimal index usage.<P>
<P>
The Plan is then passed to the <A The Plan is then passed to the <A
HREF="../../backend/executor">executor</A> for execution, and the result HREF="../../backend/executor">executor</A> for execution, and the result
returned to the client. The Plan actually as set of nodes, arranged in returned to the client. The Plan actually as set of nodes, arranged in
a tree structure with a top-level node, and various sub-nodes as a tree structure with a top-level node, and various sub-nodes as
children. children.<P>
<P>
There are many other modules that support this basic functionality.
They can be accessed by clicking on the flowchart.
<P>
<HR> There are many other modules that support this basic functionality. They
<P> can be accessed by clicking on the flowchart.<P>
<HR><P>
Another area of interest is the shared memory area, which contains data Another area of interest is the shared memory area, which contains data
accessable to all backends. It has table recently used data/index accessable to all backends. It has table recently used data/index
blocks, locks, backend information, and lookup tables for these blocks, locks, backend information, and lookup tables for these
structures: structures:
<UL> <UL>
<LI>ShmemIndex - lookup shared memory addresses using structure names <LI>ShmemIndex - lookup shared memory addresses using structure names
<LI><A HREF="../../include/storage/buf_internals.h">Buffer <LI><A HREF="../../include/storage/buf_internals.h">Buffer
Descriptor</A> - control header for buffer cache block Descriptor</A> - control header for buffer cache block
<LI><A HREF="../../include/storage/buf_internals.h">Buffer Block</A> - <LI><A HREF="../../include/storage/buf_internals.h">Buffer Block</A> -
data/index buffer cache block data/index buffer cache block
<LI>Shared Buffer Lookup Table - lookup of buffer cache block addresses using <LI>Shared Buffer Lookup Table - lookup of buffer cache block addresses
table name and block number(<A HREF="../../include/storage/buf_internals.h"> using table name and block number(<A
BufferTag</A>) HREF="../../include/storage/buf_internals.h"> BufferTag</A>)
<LI>MultiLevelLockTable (ctl) - control structure for <LI>MultiLevelLockTable (ctl) - control structure for each locking
each locking method. Currently, only multi-level locking is used(<A method. Currently, only multi-level locking is used(<A
HREF="../../include/storage/lock.h">LOCKMETHODCTL</A>). HREF="../../include/storage/lock.h">LOCKMETHODCTL</A>).
<LI>MultiLevelLockTable (lock hash) - the <A <LI>MultiLevelLockTable (lock hash) - the <A
HREF="../../include/storage/lock.h">LOCK</A> structure, looked up using HREF="../../include/storage/lock.h">LOCK</A> structure, looked up using
relation, database object ids(<A relation, database object ids(<A
HREF="../../include/storage/lock.h">LOCKTAG)</A>. The lock table structure contains the HREF="../../include/storage/lock.h">LOCKTAG)</A>. The lock table
lock modes(read/write or shared/exclusive) and circular linked list of backends (<A structure contains the lock modes(read/write or shared/exclusive) and
circular linked list of backends (<A
HREF="../../include/storage/proc.h">PROC</A> structure pointers) waiting HREF="../../include/storage/proc.h">PROC</A> structure pointers) waiting
on the lock. on the lock.
<LI>MultiLevelLockTable (xid hash) - lookup of LOCK structure address <LI>MultiLevelLockTable (xid hash) - lookup of LOCK structure address
@ -152,11 +151,12 @@ contains a pointer to the backend's PROC.lockQueue.
<LI><A HREF="../../include/storage/proc.h">Proc Header</A> - information <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> </UL>
Each data structure is created by calling <A Each data structure is created by calling <A
HREF="../../backend/storage/ipc/shmem.c">ShmemInitStruct(),</A> and HREF="../../backend/storage/ipc/shmem.c">ShmemInitStruct(),</A> and the
the lookups are created by lookups are created by <A
<A HREF="../../backend/storage/ipc/shmem.c">ShmemInitHash().</A> HREF="../../backend/storage/ipc/shmem.c">ShmemInitHash().</A><P>
<P>
<HR SIZE="2" NOSHADE> <HR SIZE="2" NOSHADE>
<SMALL> <SMALL>