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Bruce Momjian 1998-07-21 04:48:31 +00:00
parent 7f61f8a71f
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src/tools/backend/index.html
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@ -43,37 +43,35 @@ Click on an item to see more detail or look at the full
<HR>
<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
the
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 the
<A HREF="../../backend/parser">parser,</A> where the lexical scanner,
<A HREF="../../backend/parser/scan.l">scan.l,</A>
breaks the query up into tokens(words). The parser
uses
<A HREF="../../backend/parser/gram.y">gram.y</A> and the tokens to
identify the query type, and load the proper query-specific structure,
like <A HREF="../../include/nodes/parsenodes.h">CreateStmt</A> or <A
HREF="../../include/nodes/parsenodes.h">SelectStmt.</A>
<P>
<A HREF="../../backend/parser/scan.l">scan.l,</A> breaks the query up
into tokens(words). The parser uses <A
HREF="../../backend/parser/gram.y">gram.y</A> and the tokens to identify
the query type, and load the proper query-specific structure, like <A
HREF="../../include/nodes/parsenodes.h">CreateStmt</A> or <A
HREF="../../include/nodes/parsenodes.h">SelectStmt.</A><P>
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
in <A HREF="../../backend/commands"> commands.</A> A complex query, like
<I>SELECT, UPDATE,</I> and
<I>DELETE</I> requires much more handling.
<P>
<I>SELECT, UPDATE,</I> and <I>DELETE</I> 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
<I>WHERE</I> clause qualification, which is filled in by
<A HREF="../../backend/parser/parse_clause.c">transformWhereClause().</A>
<I>WHERE</I> 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
are linked together to form the <I>range table</I> of the query, which is
generated by <A HREF="../../backend/parser/parse_clause.c">
makeRangeTable().</A> Query.rtable holds the query's range table.
<P>
are linked together to form the <I>range table</I> of the query, which
is generated by <A HREF="../../backend/parser/parse_clause.c">
makeRangeTable().</A> Query.rtable holds the query's range table.<P>
Certain queries, like <I>SELECT,</I> return columns of data. Other
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
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
generated by
<A HREF="../../backend/parser/parse_target.c">transformTargetList().</A>
<P>
generated by <A
HREF="../../backend/parser/parse_target.c">transformTargetList().</A><P>
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.
<P>
and <I>ORDER BY</I> are also stored in their own Query fields.<P>
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
HREF="../../backend/rewrite">rewrite</A> system.
<P>
HREF="../../backend/rewrite">rewrite</A> system.<P>
The <A HREF="../../backend/optimizer">optimizer</A> takes the Query
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
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(<I>WHERE</I> clause) to consider optimal index usage.
<P>
Query.qual(<I>WHERE</I> 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
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
children.
<P>
children.<P>
There are many other modules that support this basic functionality.
They can be accessed by clicking on the flowchart.
<P>
<HR>
<P>
There are many other modules that support this basic functionality. They
can be accessed by clicking on the flowchart.<P>
<HR><P>
Another area of interest is the shared memory area, which contains data
accessable to all backends. It has table recently used data/index
blocks, locks, backend information, and lookup tables for these
structures:
<UL>
<LI>ShmemIndex - lookup shared memory addresses using structure names
<LI><A HREF="../../include/storage/buf_internals.h">Buffer
Descriptor</A> - control header for buffer cache block
<LI><A HREF="../../include/storage/buf_internals.h">Buffer Block</A> -
data/index buffer cache block
<LI>Shared Buffer Lookup Table - lookup of buffer cache block addresses using
table name and block number(<A HREF="../../include/storage/buf_internals.h">
BufferTag</A>)
<LI>MultiLevelLockTable (ctl) - control structure for
each locking method. Currently, only multi-level locking is used(<A
<LI>Shared Buffer Lookup Table - lookup of buffer cache block addresses
using table name and block number(<A
HREF="../../include/storage/buf_internals.h"> BufferTag</A>)
<LI>MultiLevelLockTable (ctl) - control structure for each locking
method. Currently, only multi-level locking is used(<A
HREF="../../include/storage/lock.h">LOCKMETHODCTL</A>).
<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 or shared/exclusive) and circular linked list of backends (<A
HREF="../../include/storage/lock.h">LOCKTAG)</A>. The lock table
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
on the lock.
<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
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
the lookups are created by
<A HREF="../../backend/storage/ipc/shmem.c">ShmemInitHash().</A>
<P>
HREF="../../backend/storage/ipc/shmem.c">ShmemInitStruct(),</A> and the
lookups are created by <A
HREF="../../backend/storage/ipc/shmem.c">ShmemInitHash().</A><P>
<HR SIZE="2" NOSHADE>
<SMALL>