<AHREF="../../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

<AHREF="../../backend/parser/parse_clause.c">transformWhereClause().</A>

Each table is represented by a<AHREF="../../include/nodes/parsenodes.h">

RangeTableEntry,</A>

and theyare linked together to form the<I>range table</I>for the

query, and isgenerated by<AHREF="../../backend/parser/parse_clause.c">

Each tablereferenced in the queryis 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<AHREF="../../backend/parser/parse_clause.c">

makeRangeTable().</A> Query.rtable holds the queries range table.

Certain queries, like SELECT, return columns of data. Other queries,

like INSERT and UPDATE, specify the columns modified by the query.

Thesecolumns references are converted to<A

Thesecolumn 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

target list is stored in Query.targetList,which is generated by

<AHREF="../../backend/parser/parse_target.c">transformTargetList().</A>

Other query elements, like aggregates(SUM()), GROUP BY, ORDER BY are

also stored in their own fields.

also stored in their ownQueryfields.

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.

The optimizer takes the Query structure, and generates an optimal

<AHREF="../..//include/nodes/plannodes.h">Plan</A> containing primitive

operations to be performed by the executor to complete the query. The

<AHREF="../../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

The<AHREF="../../backend/optimizer">optimizer</A> takes the Query

structure, and generates an optimal

<AHREF="../..//include/nodes/plannodes.h">Plan</A> containing the

primitive operations to be performed by the executor to execute the

query. The<AHREF="../../backend/optimizer/path">path</A> 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.

The Plan is then passed to the<A

<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><AHREF="../../include/storage/buf_internals.h">Buffer

Descriptors</A> - control header for shared memory buffer block

<LI><AHREF="../../include/storage/buf_internals.h">Buffer Blocks</A>

- 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

<LI><AHREF="../../include/storage/lock.h">LockTable</A>

- 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

<LI><AHREF="../../include/storage/proc.h">Proc Header</A> - information

about each backend, including locks held/waiting,indexed by process id

Each structure is created by calling<A

HREF="../../backend/storage/ipc/shmem.c"> ShmemInitStruct().</A>

Each data structure is created by calling<A

HREF="../../backend/storage/ipc/shmem.c"> ShmemInitStruct(),</A> and

the lookup hashes are created by

<AHREF="../../backend/storage/ipc/shmem.c">ShmemInitHash().</A>