diff options
Diffstat (limited to 'src/tools/backend/index.html')
| -rw-r--r-- | src/tools/backend/index.html | 97 |
1 files changed, 92 insertions, 5 deletions
diff --git a/src/tools/backend/index.html b/src/tools/backend/index.html index 04166222afb..e286b6d8c66 100644 --- a/src/tools/backend/index.html +++ b/src/tools/backend/index.html @@ -9,8 +9,90 @@ PostgreSQL Backend Flowchart <H2 ALIGN=CENTER> by Bruce Momjian </H2 ALIGN=CENTER> +<P> +Queries come into the backend via data packets coming in through TCP/IP +and Unix Domain sockets. They are 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-type-specific +structure, like +<A HREF="../../include/nodes/parsenodes.h">CreateStmt or SelectStmt.</A> +<P> +The query is then identified as a <I>Utility</I> function or a more +complex query. <I>Utility</I> queries are processed by a +query-type-specific function in <A HREF="../../backend/commands"> +commands.</A> Complex queries, like <I>SELECT, UPDATE,</I> and +<I>DELETE</I> require much more handling. +<P> +The parser takes the complex queries, 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 +WHERE clause qualification, which is filled in by + +<A HREF="../../backend/parser/parse_clause.c">transformWhereClause().</A> +Each table is represented by a <A HREF="../../include/nodes/parsenodes.h"> +RangeTableEntry,</A> +and they are linked together to form the <I>range table</I> for the +query, and is generated by <A HREF="../../backend/parser/parse_clause.c"> +makeRangeTable().</A> Query.rtable holds the queries range table. +<P> +Certain queries, like SELECT, return columns of data. Other queries, +like INSERT and UPDATE, specify the columns modified by the query. +These columns 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, and is generated by +<A HREF="../../backend/parser/parse_target.c">transformTargetList().</A> +<P> +Other query elements, like aggregates(SUM()), GROUP BY, ORDER BY are +also stored in their own fields. +<P> +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 <A +HREF="../../backend/rewrite">rewrite</A> system. +<P> +The optimizer takes the Query structure, and generates an optimal +<A HREF="../..//include/nodes/plannodes.h">Plan</A> containing primitive +operations to be performed by the executor to complete the query. The +<A HREF="../../backend/optimizer/path">path</A> module +determines the table join order and join type of each of the tables in +the RangeTable, using Query.qual(WHERE 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 +is returned to the client. +<P> +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 data/index blocks, locks, and backend information: +<UL> +<LI>ShmemIndex - contains an index of all other shared memory +structures, allowing quick lookup of other structure locations in shared +memory +<LI>Buffer Descriptors - control header for shared memory buffer block +<LI>Buffer Blocks - block of table/index data shared by all backends +<LI>Shared Buf Lookup Table - lookup to see if a requested buffer +is already in the shared memory area +<LI>LockTable - lock table structure, specifiying table, lock types, and +backends holding or waiting on lock +<LI>LockTable (lock hash) - lookup of LockTable structures using +table name +<LI>LockTable (xid hash) - lookup of LockTable structures using +transaction id +<LI>Proc Header - information about each backend, including locks held/waiting, +indexed by process id +</UL> +Each structure is created by calling <A +HREF="../../backend/storage/ipc/shmem.c"> ShmemInitStruct().</A> +<HR> <CENTER> -<BR> <EM><BIG> Click on an item to see more detail or click <A HREF="backend_dirs.html">here</a> to see the full index. @@ -38,9 +120,14 @@ Click on an item to see more detail or click <AREA COORDS="10,510,170,550" HREF="backend_dirs.html#nodes"> <AREA COORDS="10,570,170,610" HREF="backend_dirs.html#storage"> </MAP> -<HR> +<BR> +<HR SIZE="2" NOSHADE> +<SMALL> <ADDRESS> -Maintainer: Bruce Momjian<A -HREF="mailto:maillist@candle.pha.pa.us">maillist@candle.pha.pa.us</a>)<BR> -Last updated: Mon Oct 27 11:01:08 EST 1997 +Maintainer: Bruce Momjian (<A +HREF="mailto:maillist@candle.pha.pa.us">maillist@candle.pha.pa.us</A>)<BR> +Last updated: Tue Dec 9 17:56:08 EST 1997 </ADDRESS> +</SMALL> +</BODY> +</HTML> |