From 224a62c5b793bcc6ddf7c3b8e6301e6c5fa23ee9 Mon Sep 17 00:00:00 2001 From: Bruce Momjian Date: Tue, 21 Jul 1998 04:48:31 +0000 Subject: [PATCH] Update. --- src/tools/backend/index.html | 94 ++++++++++++++++++------------------ 1 file changed, 47 insertions(+), 47 deletions(-) diff --git a/src/tools/backend/index.html b/src/tools/backend/index.html index 51e4972037..300061deae 100644 --- a/src/tools/backend/index.html +++ b/src/tools/backend/index.html @@ -43,37 +43,35 @@ Click on an item to see more detail or look at the full

-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 parser, where the lexical scanner, -scan.l, -breaks the query up into tokens(words). The parser -uses -gram.y and the tokens to -identify the query type, and load the proper query-specific structure, -like CreateStmt or SelectStmt. -

+scan.l, breaks the query up +into tokens(words). The parser uses gram.y and the tokens to identify +the query type, and load the proper query-specific structure, like CreateStmt or SelectStmt.

+ The query is then identified as a Utility query or a more complex query. A Utility query is processed by a query-specific function in commands. A complex query, like -SELECT, UPDATE, and -DELETE requires much more handling. -

+SELECT, UPDATE, and DELETE requires much more handling.

+ The parser takes a complex query, and creates a Query structure that contains all the elements used by complex queries. Query.qual holds the -WHERE clause qualification, which is filled in by -transformWhereClause(). +WHERE clause qualification, which is filled in by transformWhereClause(). Each table referenced in the query is represented by a RangeTableEntry, and they -are linked together to form the range table of the query, which is -generated by -makeRangeTable(). Query.rtable holds the query's range table. -

+are linked together to form the range table of the query, which +is generated by +makeRangeTable(). Query.rtable holds the query's range table.

+ Certain queries, like SELECT, return columns of data. Other queries, like INSERT and UPDATE, specify the columns @@ -82,18 +80,18 @@ HREF="../../include/nodes/primnodes.h">Resdom entries, which are placed in target list entries, and linked together to make up the target list of the query. The target list is stored in Query.targetList, which is -generated by -transformTargetList(). -

+generated by transformTargetList().

+ Other query elements, like aggregates(SUM()), GROUP BY, -and ORDER BY are also stored in their own Query fields. -

+and ORDER BY are also stored in their own Query fields.

+ The next step is for the Query to be modified by any VIEWS or RULES that may apply to the query. This is performed by the rewrite system. -

+HREF="../../backend/rewrite">rewrite system.

+ The optimizer takes the Query structure and generates an optimal Plan, which contains the operations to be performed to execute the query. The path module determines the best table join order and join type of each table in the RangeTable, using -Query.qual(WHERE clause) to consider optimal index usage. -

+Query.qual(WHERE clause) to consider optimal index usage.

The Plan is then passed to the executor 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. -

+children.

-There are many other modules that support this basic functionality. -They can be accessed by clicking on the flowchart. -

-

-

+There are many other modules that support this basic functionality. They +can be accessed by clicking on the flowchart.

+ + +

+ 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: +

+ Each data structure is created by calling ShmemInitStruct(), and -the lookups are created by -ShmemInitHash(). -

+HREF="../../backend/storage/ipc/shmem.c">ShmemInitStruct(), and the +lookups are created by ShmemInitHash().

+