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discussion of 5/19/00). pg_index is now searched for indexes of a relation using an indexscan. Moreover, this is done once and cached in the relcache entry for the relation, in the form of a list of OIDs for the indexes. This list is used by the parser and executor to drive lookups in the pg_index syscache when they want to know the properties of the indexes. Net result: index information will be fully cached for repetitive operations such as inserts.
This directory does more than tokenize and parse SQL queries. It also creates Query structures for the various complex queries that is passed to the optimizer and then executor. parser.c things start here scan.l break query into tokens scansup.c handle escapes in input keywords.c turn keywords into specific tokens gram.y parse the tokens and fill query-type-specific structures analyze.c handle post-parse processing for each query type parse_clause.c handle clauses like WHERE, ORDER BY, GROUP BY, ... parse_coerce.c used for coercing expressions of different types parse_expr.c handle expressions like col, col + 3, x = 3 or x = 4 parse_oper.c handle operations in expressions parse_agg.c handle aggregates, like SUM(col1), AVG(col2), ... parse_func.c handle functions, table.column and column identifiers parse_node.c create nodes for various structures parse_target.c handle the result list of the query parse_relation.c support routines for tables and column handling parse_type.c support routines for type handling