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Let ALTER TABLE Phase 2 routines manage the relation pointer

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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
This commit is contained in:
Alvaro Herrera 2021-03-25 15:56:11 -03:00
parent 4669cacbd4
commit cd03c6e94b
No known key found for this signature in database
GPG Key ID: 1C20ACB9D5C564AE
1 changed files with 13 additions and 6 deletions
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19
src/backend/commands/tablecmds.c
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@ -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;