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Add a function lastval(), which returns the value returned by the

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last nextval() or setval() performed by the current session. Update the
docs, add regression tests, and bump the catalog version. Patch from
Dennis Björklund, various improvements by Neil Conway.
This commit is contained in:
Neil Conway
2005-06-07 07:08:35 +00:00
parent c59887f916
commit 657c098e41
7 changed files with 202 additions and 36 deletions
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114
src/backend/commands/sequence.c
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@ -8,7 +8,7 @@
*
*
* IDENTIFICATION
* $PostgreSQL: pgsql/src/backend/commands/sequence.c,v 1.122 2005/06/06 20:22:57 tgl Exp $
* $PostgreSQL: pgsql/src/backend/commands/sequence.c,v 1.123 2005/06/07 07:08:34 neilc Exp $
*
*-------------------------------------------------------------------------
*/
@ -24,6 +24,7 @@
#include "utils/acl.h"
#include "utils/builtins.h"
#include "utils/resowner.h"
#include "utils/syscache.h"
/*
@ -68,7 +69,13 @@ typedef SeqTableData *SeqTable;
static SeqTable seqtab = NULL; /* Head of list of SeqTable items */
/*
* last_used_seq is updated by nextval() to point to the last used
* sequence.
*/
static SeqTableData *last_used_seq = NULL;
static void acquire_share_lock(Relation seqrel, SeqTable seq);
static void init_sequence(RangeVar *relation,
SeqTable *p_elm, Relation *p_rel);
static Form_pg_sequence read_info(SeqTable elm, Relation rel, Buffer *buf);
@ -400,6 +407,7 @@ nextval(PG_FUNCTION_ARGS)
if (elm->last != elm->cached) /* some numbers were cached */
{
last_used_seq = elm;
elm->last += elm->increment;
relation_close(seqrel, NoLock);
PG_RETURN_INT64(elm->last);
@ -521,6 +529,8 @@ nextval(PG_FUNCTION_ARGS)
elm->last = result; /* last returned number */
elm->cached = last; /* last fetched number */
last_used_seq = elm;
START_CRIT_SECTION();
/* XLOG stuff */
@ -602,6 +612,42 @@ currval(PG_FUNCTION_ARGS)
PG_RETURN_INT64(result);
}
Datum
lastval(PG_FUNCTION_ARGS)
{
Relation seqrel;
int64 result;
if (last_used_seq == NULL)
ereport(ERROR,
(errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
errmsg("lastval is not yet defined in this session")));
/* Someone may have dropped the sequence since the last nextval() */
if (!SearchSysCacheExists(RELOID,
ObjectIdGetDatum(last_used_seq->relid),
0, 0, 0))
ereport(ERROR,
(errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
errmsg("lastval is not yet defined in this session")));
seqrel = relation_open(last_used_seq->relid, NoLock);
acquire_share_lock(seqrel, last_used_seq);
/* nextval() must have already been called for this sequence */
Assert(last_used_seq->increment != 0);
if (pg_class_aclcheck(last_used_seq->relid, GetUserId(), ACL_SELECT) != ACLCHECK_OK)
ereport(ERROR,
(errcode(ERRCODE_INSUFFICIENT_PRIVILEGE),
errmsg("permission denied for sequence %s",
RelationGetRelationName(seqrel))));
result = last_used_seq->last;
relation_close(seqrel, NoLock);
PG_RETURN_INT64(result);
}
/*
* Main internal procedure that handles 2 & 3 arg forms of SETVAL.
*
@ -740,6 +786,41 @@ setval_and_iscalled(PG_FUNCTION_ARGS)
}
/*
* If we haven't touched the sequence already in this transaction,
* we need to acquire AccessShareLock. We arrange for the lock to
* be owned by the top transaction, so that we don't need to do it
* more than once per xact.
*/
static void
acquire_share_lock(Relation seqrel, SeqTable seq)
{
TransactionId thisxid = GetTopTransactionId();
if (seq->xid != thisxid)
{
ResourceOwner currentOwner;
currentOwner = CurrentResourceOwner;
PG_TRY();
{
CurrentResourceOwner = TopTransactionResourceOwner;
LockRelation(seqrel, AccessShareLock);
}
PG_CATCH();
{
/* Ensure CurrentResourceOwner is restored on error */
CurrentResourceOwner = currentOwner;
PG_RE_THROW();
}
PG_END_TRY();
CurrentResourceOwner = currentOwner;
/* Flag that we have a lock in the current xact. */
seq->xid = thisxid;
}
}
/*
* Given a relation name, open and lock the sequence. p_elm and p_rel are
* output parameters.
@ -748,7 +829,6 @@ static void
init_sequence(RangeVar *relation, SeqTable *p_elm, Relation *p_rel)
{
Oid relid = RangeVarGetRelid(relation, false);
TransactionId thisxid = GetTopTransactionId();
volatile SeqTable elm;
Relation seqrel;
@ -796,35 +876,7 @@ init_sequence(RangeVar *relation, SeqTable *p_elm, Relation *p_rel)
seqtab = elm;
}
/*
* If we haven't touched the sequence already in this transaction,
* we need to acquire AccessShareLock. We arrange for the lock to
* be owned by the top transaction, so that we don't need to do it
* more than once per xact.
*/
if (elm->xid != thisxid)
{
ResourceOwner currentOwner;
currentOwner = CurrentResourceOwner;
PG_TRY();
{
CurrentResourceOwner = TopTransactionResourceOwner;
LockRelation(seqrel, AccessShareLock);
}
PG_CATCH();
{
/* Ensure CurrentResourceOwner is restored on error */
CurrentResourceOwner = currentOwner;
PG_RE_THROW();
}
PG_END_TRY();
CurrentResourceOwner = currentOwner;
/* Flag that we have a lock in the current xact. */
elm->xid = thisxid;
}
acquire_share_lock(seqrel, elm);
*p_elm = elm;
*p_rel = seqrel;