postgres.git / summary / log / commit / refs

commit    cd03c6e94b09ff402cbc3ce8da5587f09f0b5e58
Author:   Alvaro Herrera <alvherre@alvh.no-ip.org>
Date:     Thu Mar 25 18:56:11 2021 +0000
First released in: 14.0

    Let ALTER TABLE Phase 2 routines manage the relation pointer
    
    Struct AlteredRelationInfo gains a new Relation member, to be used only
    by Phase 2 (ATRewriteCatalogs); this allows ATExecCmd() subroutines open
    and close the relation internally.
    
    A future commit will use this facility to implement an ALTER TABLE
    subcommand that closes and reopens the relation across transaction
    boundaries.
    
    (It is possible to keep the relation open past phase 2 to be used by
    phase 3 instead of having to reopen it that point, but there are some
    minor complications with that; it's not clear that there is much to be
    won from doing that, though.)
    
    Author: Álvaro Herrera <alvherre@alvh.no-ip.org>
    Discussion: https://postgr.es/m/20200803234854.GA24158@alvherre.pgsql


 src/backend/commands/tablecmds.c | 19 +++++++++++++------
 1 file changed, 13 insertions(+), 6 deletions(-)

diff --git a/src/backend/commands/tablecmds.c b/src/backend/commands/tablecmds.c
index 3349bcfaa74..bf7fd6e8ae6 100644
--- a/src/backend/commands/tablecmds.c
+++ b/src/backend/commands/tablecmds.c
@@ -157,6 +157,8 @@ typedef struct AlteredTableInfo
 	Oid			relid;			/* Relation to work on */
 	char		relkind;		/* Its relkind */
 	TupleDesc	oldDesc;		/* Pre-modification tuple descriptor */
+	/* Transiently set during Phase 2, normally set to NULL */
+	Relation	rel;
 	/* Information saved by Phase 1 for Phase 2: */
 	List	   *subcmds[AT_NUM_PASSES]; /* Lists of AlterTableCmd */
 	/* Information saved by Phases 1/2 for Phase 3: */
@@ -354,7 +356,7 @@ static void ATPrepCmd(List **wqueue, Relation rel, AlterTableCmd *cmd,
 					  AlterTableUtilityContext *context);
 static void ATRewriteCatalogs(List **wqueue, LOCKMODE lockmode,
 							  AlterTableUtilityContext *context);
-static void ATExecCmd(List **wqueue, AlteredTableInfo *tab, Relation rel,
+static void ATExecCmd(List **wqueue, AlteredTableInfo *tab,
 					  AlterTableCmd *cmd, LOCKMODE lockmode, int cur_pass,
 					  AlterTableUtilityContext *context);
 static AlterTableCmd *ATParseTransformCmd(List **wqueue, AlteredTableInfo *tab,
@@ -4569,7 +4571,6 @@ ATRewriteCatalogs(List **wqueue, LOCKMODE lockmode,
 		{
 			AlteredTableInfo *tab = (AlteredTableInfo *) lfirst(ltab);
 			List	   *subcmds = tab->subcmds[pass];
-			Relation	rel;
 			ListCell   *lcmd;
 
 			if (subcmds == NIL)
@@ -4578,10 +4579,10 @@ ATRewriteCatalogs(List **wqueue, LOCKMODE lockmode,
 			/*
 			 * Appropriate lock was obtained by phase 1, needn't get it again
 			 */
-			rel = relation_open(tab->relid, NoLock);
+			tab->rel = relation_open(tab->relid, NoLock);
 
 			foreach(lcmd, subcmds)
-				ATExecCmd(wqueue, tab, rel,
+				ATExecCmd(wqueue, tab,
 						  castNode(AlterTableCmd, lfirst(lcmd)),
 						  lockmode, pass, context);
 
@@ -4593,7 +4594,11 @@ ATRewriteCatalogs(List **wqueue, LOCKMODE lockmode,
 			if (pass == AT_PASS_ALTER_TYPE)
 				ATPostAlterTypeCleanup(wqueue, tab, lockmode);
 
-			relation_close(rel, NoLock);
+			if (tab->rel)
+			{
+				relation_close(tab->rel, NoLock);
+				tab->rel = NULL;
+			}
 		}
 	}
 
@@ -4619,11 +4624,12 @@ ATRewriteCatalogs(List **wqueue, LOCKMODE lockmode,
  * ATExecCmd: dispatch a subcommand to appropriate execution routine
  */
 static void
-ATExecCmd(List **wqueue, AlteredTableInfo *tab, Relation rel,
+ATExecCmd(List **wqueue, AlteredTableInfo *tab,
 		  AlterTableCmd *cmd, LOCKMODE lockmode, int cur_pass,
 		  AlterTableUtilityContext *context)
 {
 	ObjectAddress address = InvalidObjectAddress;
+	Relation	rel = tab->rel;
 
 	switch (cmd->subtype)
 	{
@@ -5730,6 +5736,7 @@ ATGetQueueEntry(List **wqueue, Relation rel)
 	 */
 	tab = (AlteredTableInfo *) palloc0(sizeof(AlteredTableInfo));
 	tab->relid = relid;
+	tab->rel = NULL;			/* set later */
 	tab->relkind = rel->rd_rel->relkind;
 	tab->oldDesc = CreateTupleDescCopyConstr(RelationGetDescr(rel));
 	tab->newrelpersistence = RELPERSISTENCE_PERMANENT;


[parent: 4669cacbd4b4]