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If the join problem's entire ORDER BY clause can be pushed to the remote server, consider a path that adds this ORDER BY clause. If use_remote_estimate is on, we cost this path using an additional remote EXPLAIN. If not, we just estimate that the path costs 20% more, which is intended to be large enough that we won't request a remote sort when it's not helpful, but small enough that we'll have the remote side do the sort when in doubt. In some cases, the remote sort might actually be free, because the remote query plan might happen to produce output that is ordered the way we need, but without remote estimates we have no way of knowing that. It might also be useful to request sorted output from the remote side if it enables an efficient merge join, but this patch doesn't attempt to handle that case. Ashutosh Bapat with revisions by me. Also reviewed by Fabrízio de Royes Mello and Jeevan Chalke.
82 lines
2.7 KiB
C
82 lines
2.7 KiB
C
/*-------------------------------------------------------------------------
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*
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* postgres_fdw.h
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* Foreign-data wrapper for remote PostgreSQL servers
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*
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* Portions Copyright (c) 2012-2015, PostgreSQL Global Development Group
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*
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* IDENTIFICATION
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* contrib/postgres_fdw/postgres_fdw.h
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*
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*-------------------------------------------------------------------------
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*/
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#ifndef POSTGRES_FDW_H
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#define POSTGRES_FDW_H
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#include "foreign/foreign.h"
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#include "lib/stringinfo.h"
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#include "nodes/relation.h"
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#include "utils/relcache.h"
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#include "libpq-fe.h"
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/* in postgres_fdw.c */
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extern int set_transmission_modes(void);
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extern void reset_transmission_modes(int nestlevel);
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/* in connection.c */
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extern PGconn *GetConnection(ForeignServer *server, UserMapping *user,
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bool will_prep_stmt);
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extern void ReleaseConnection(PGconn *conn);
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extern unsigned int GetCursorNumber(PGconn *conn);
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extern unsigned int GetPrepStmtNumber(PGconn *conn);
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extern void pgfdw_report_error(int elevel, PGresult *res, PGconn *conn,
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bool clear, const char *sql);
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/* in option.c */
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extern int ExtractConnectionOptions(List *defelems,
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const char **keywords,
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const char **values);
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/* in deparse.c */
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extern void classifyConditions(PlannerInfo *root,
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RelOptInfo *baserel,
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List *input_conds,
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List **remote_conds,
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List **local_conds);
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extern bool is_foreign_expr(PlannerInfo *root,
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RelOptInfo *baserel,
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Expr *expr);
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extern void deparseSelectSql(StringInfo buf,
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PlannerInfo *root,
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RelOptInfo *baserel,
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Bitmapset *attrs_used,
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List **retrieved_attrs);
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extern void appendWhereClause(StringInfo buf,
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PlannerInfo *root,
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RelOptInfo *baserel,
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List *exprs,
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bool is_first,
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List **params);
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extern void deparseInsertSql(StringInfo buf, PlannerInfo *root,
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Index rtindex, Relation rel,
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List *targetAttrs, bool doNothing, List *returningList,
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List **retrieved_attrs);
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extern void deparseUpdateSql(StringInfo buf, PlannerInfo *root,
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Index rtindex, Relation rel,
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List *targetAttrs, List *returningList,
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List **retrieved_attrs);
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extern void deparseDeleteSql(StringInfo buf, PlannerInfo *root,
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Index rtindex, Relation rel,
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List *returningList,
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List **retrieved_attrs);
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extern void deparseAnalyzeSizeSql(StringInfo buf, Relation rel);
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extern void deparseAnalyzeSql(StringInfo buf, Relation rel,
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List **retrieved_attrs);
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extern void deparseStringLiteral(StringInfo buf, const char *val);
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extern Expr *find_em_expr_for_rel(EquivalenceClass *ec, RelOptInfo *rel);
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extern void appendOrderByClause(StringInfo buf, PlannerInfo *root,
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RelOptInfo *baserel, List *pathkeys);
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#endif /* POSTGRES_FDW_H */
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