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robertmhaasrobertmhaas
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postgres_fdw: Refactor deparsing code for locking clauses.
The upcoming patch to allow join pushdown in postgres_fdw needs to use this code multiple times, which requires moving it to deparse.c. That seems like a good idea anyway, so do that now both on general principle and to simplify the future patch. Inspired by a patch by Shigeru Hanada and Ashutosh Bapat, but I did it a little differently than what that patch did.
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-49
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3 files changed

+64
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‎contrib/postgres_fdw/deparse.c

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Original file line numberDiff line numberDiff line change
@@ -45,7 +45,9 @@
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#include "catalog/pg_type.h"
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#include "commands/defrem.h"
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#include "nodes/nodeFuncs.h"
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#include "nodes/plannodes.h"
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#include "optimizer/clauses.h"
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#include "optimizer/prep.h"
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#include "optimizer/var.h"
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#include "parser/parsetree.h"
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#include "utils/builtins.h"
@@ -807,6 +809,64 @@ deparseTargetList(StringInfo buf,
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appendStringInfoString(buf, "NULL");
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}
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/*
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* Deparse the appropriate locking clause (FOR SELECT or FOR SHARE) for a
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* given relation.
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*/
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void
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deparseLockingClause(StringInfo buf, PlannerInfo *root, RelOptInfo *rel)
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{
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/*
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* Add FOR UPDATE/SHARE if appropriate. We apply locking during the
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* initial row fetch, rather than later on as is done for local tables.
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* The extra roundtrips involved in trying to duplicate the local
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* semantics exactly don't seem worthwhile (see also comments for
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* RowMarkType).
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*
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* Note: because we actually run the query as a cursor, this assumes that
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* DECLARE CURSOR ... FOR UPDATE is supported, which it isn't before 8.3.
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*/
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if (rel->relid == root->parse->resultRelation &&
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(root->parse->commandType == CMD_UPDATE ||
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root->parse->commandType == CMD_DELETE))
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{
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/* Relation is UPDATE/DELETE target, so use FOR UPDATE */
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appendStringInfoString(buf, " FOR UPDATE");
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}
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else
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{
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PlanRowMark *rc = get_plan_rowmark(root->rowMarks, rel->relid);
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if (rc)
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{
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/*
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* Relation is specified as a FOR UPDATE/SHARE target, so handle
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* that. (But we could also see LCS_NONE, meaning this isn't a
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* target relation after all.)
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*
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* For now, just ignore any [NO] KEY specification, since (a) it's
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* not clear what that means for a remote table that we don't have
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* complete information about, and (b) it wouldn't work anyway on
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* older remote servers. Likewise, we don't worry about NOWAIT.
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*/
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switch (rc->strength)
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{
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case LCS_NONE:
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/* No locking needed */
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break;
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case LCS_FORKEYSHARE:
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case LCS_FORSHARE:
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appendStringInfoString(buf, " FOR SHARE");
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break;
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case LCS_FORNOKEYUPDATE:
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case LCS_FORUPDATE:
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appendStringInfoString(buf, " FOR UPDATE");
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break;
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}
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}
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}
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}
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/*
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* Deparse WHERE clauses in given list of RestrictInfos and append them to buf.
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*

‎contrib/postgres_fdw/postgres_fdw.c

Lines changed: 2 additions & 49 deletions
Original file line numberDiff line numberDiff line change
@@ -1013,55 +1013,8 @@ postgresGetForeignPlan(PlannerInfo *root,
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if (best_path->path.pathkeys)
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appendOrderByClause(&sql, root, baserel, best_path->path.pathkeys);
10151015

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/*
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* Add FOR UPDATE/SHARE if appropriate. We apply locking during the
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* initial row fetch, rather than later on as is done for local tables.
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* The extra roundtrips involved in trying to duplicate the local
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* semantics exactly don't seem worthwhile (see also comments for
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* RowMarkType).
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*
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* Note: because we actually run the query as a cursor, this assumes that
1024-
* DECLARE CURSOR ... FOR UPDATE is supported, which it isn't before 8.3.
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*/
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if (baserel->relid == root->parse->resultRelation &&
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(root->parse->commandType == CMD_UPDATE ||
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root->parse->commandType == CMD_DELETE))
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{
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/* Relation is UPDATE/DELETE target, so use FOR UPDATE */
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appendStringInfoString(&sql, " FOR UPDATE");
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}
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else
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{
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PlanRowMark *rc = get_plan_rowmark(root->rowMarks, baserel->relid);
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if (rc)
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{
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/*
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* Relation is specified as a FOR UPDATE/SHARE target, so handle
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* that. (But we could also see LCS_NONE, meaning this isn't a
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* target relation after all.)
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*
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* For now, just ignore any [NO] KEY specification, since (a) it's
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* not clear what that means for a remote table that we don't have
1046-
* complete information about, and (b) it wouldn't work anyway on
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* older remote servers. Likewise, we don't worry about NOWAIT.
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*/
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switch (rc->strength)
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{
1051-
case LCS_NONE:
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/* No locking needed */
1053-
break;
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case LCS_FORKEYSHARE:
1055-
case LCS_FORSHARE:
1056-
appendStringInfoString(&sql, " FOR SHARE");
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break;
1058-
case LCS_FORNOKEYUPDATE:
1059-
case LCS_FORUPDATE:
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appendStringInfoString(&sql, " FOR UPDATE");
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break;
1062-
}
1063-
}
1064-
}
1016+
/* Add any necessary FOR UPDATE/SHARE. */
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deparseLockingClause(&sql, root, baserel);
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/*
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* Build the fdw_private list that will be available to the executor.

‎contrib/postgres_fdw/postgres_fdw.h

Lines changed: 2 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -88,6 +88,8 @@ extern void deparseSelectSql(StringInfo buf,
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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 deparseLockingClause(StringInfo buf,
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PlannerInfo *root, RelOptInfo *rel);
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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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