diff --git a/src/tools/backend/index.html b/src/tools/backend/index.html index e286b6d8c66..dbf78042a46 100644 --- a/src/tools/backend/index.html +++ b/src/tools/backend/index.html @@ -32,35 +32,35 @@ The parser takes the complex queries, 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(). -Each table is represented by a -RangeTableEntry, -and they are linked together to form the range table for the -query, and is generated by +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 queries range table.

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 Resdom entries, which are linked together to make up the target list 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 transformTargetList().

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

-The optimizer takes the Query structure, and generates an optimal -Plan containing primitive -operations to be performed by the executor to complete the query. The -path 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 optimizer takes the Query +structure, and generates an optimal +Plan containing the +primitive operations to be performed by the executor 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.

The Plan is then passed to the ShmemIndex - contains an index of all other shared memory structures, allowing quick lookup of other structure locations in shared memory -

  • Buffer Descriptors - control header for shared memory buffer block -
  • Buffer Blocks - block of table/index data shared by all backends +
  • Buffer +Descriptors - control header for shared memory buffer block + +
  • Buffer Blocks +- block of table/index data shared by all backends
  • Shared Buf Lookup Table - lookup to see if a requested buffer is already in the shared memory area -
  • LockTable - lock table structure, specifiying table, lock types, and +
  • LockTable +- lock table structure, specifiying table, lock types, and backends holding or waiting on lock
  • LockTable (lock hash) - lookup of LockTable structures using table name
  • LockTable (xid hash) - lookup of LockTable structures using transaction id -
  • Proc Header - information about each backend, including locks held/waiting, -indexed by process id +
  • Proc Header - information +about each backend, including locks held/waiting, indexed by process id -Each structure is created by calling ShmemInitStruct(). +Each data structure is created by calling ShmemInitStruct(), and +the lookup hashes are created by +ShmemInitHash().