update

34d59572 · Bruce Momjian · 2584029e · 34d59572
Commit 34d59572 authored 26 years ago by Bruce Momjian
--- a/src/tools/backend/index.html
+++ b/src/tools/backend/index.html
 <HTML>
 <HEAD>
-<TITLE>PostgreSQL Backend Flowchart</TITLE>
+<TITLE>How PostgreSQL Processes a Query</TITLE>
 </HEAD>
 <BODY BGCOLOR="#FFFFFF" TEXT="#000000" LINK="#FF0000" VLINK="#A00000" ALINK="#0000FF">
 <H1 ALIGN=CENTER>
-PostgreSQL Backend Flowchart
+How PostgreSQL Processes a Query
 </H1>
 <H2 ALIGN=CENTER>
 by Bruce Momjian
 </H2>
 <P>
-A query come into the backend via data packets coming in through TCP/IP
+A query comes to the backend via data packets arriving through TCP/IP
-and Unix Domain sockets.   It is loaded into a string, and passed to
+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
+identify the query type, and load the proper query-specific structure,
-structure, like
+like <A HREF="../../include/nodes/parsenodes.h">CreateStmt</A> or <A
-<A HREF="../../include/nodes/parsenodes.h">CreateStmt or SelectStmt.</A>
+HREF="../../include/nodes/parsenodes.h">SelectStmt.</A>
 <P>
-The query is then identified as a <I>Utility</I> function or a more
+The query is then identified as a <I>Utility</I> query or a more complex
-complex query.  A <I>Utility</I> query is processed by a
+query.  A <I>Utility</I> query is processed by a query-specific function
-query-specific function in <A HREF="../../backend/commands">
+in <A HREF="../../backend/commands"> commands.</A> A complex query, like
-commands.</A> A complex query, like <CODE>SELECT, UPDATE,</CODE> and
+<CODE>SELECT, UPDATE,</CODE> and
 <CODE>DELETE</CODE> requires much more handling.
 <P>
 The parser takes a complex query, and creates a
@@ -37,7 +37,7 @@ 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 queries range table.
+makeRangeTable().</A>  Query.rtable holds the query's range table.
 <P>
 Certain queries, like <CODE>SELECT,</CODE> return columns of data.  Other
 queries, like <CODE>INSERT</CODE> and <CODE>UPDATE,</CODE> specify the columns
@@ -48,7 +48,7 @@ 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(<CODE>SUM()</CODE>), <CODE>GROUP BY,</CODE>
-<CODE>ORDER BY</CODE> are also stored in their own Query fields.
+and <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 <CODE>VIEWS</CODE> or
 <CODE>RULES</CODE> that may apply to the query.  This is performed by the <A
@@ -69,21 +69,22 @@ returned to the client.
 There are many other modules that support this basic functionality.
 They can be accessed by clicking on the flowchart.
 <P>
-Another area of interest is the shared memory area, containing table
+Another area of interest is the shared memory area, which contains data
-data/index blocks, locks, backend information, and lookup tables for
+accessable to all backends.  It has table recently used data/index
-these structures:
+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
-Descriptors</A> - control header for buffer cache block
+Descriptor</A> - control header for buffer cache block
-<LI><A HREF="../../include/storage/buf_internals.h">Buffer Blocks</A> -
+<LI><A HREF="../../include/storage/buf_internals.h">Buffer Block</A> -
 data/index buffer cache block
-<LI>Shared Buf Lookup Table - lookup of buffer cache block address using
+<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) - <A
+<LI>MultiLevelLockTable (ctl) - control structure for
-HREF="../../include/storage/lock.h">LOCKCTL</A> control structure for
+each locking method.  Currently, only multi-level locking is used(<A
-each locking method.  Currently, only multi-level locking is used.
+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
@@ -105,7 +106,9 @@ 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>
 <HR>
+<P>
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