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Add pg_sequences view

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Like pg_tables, pg_views, and others, this view contains information
about sequences in a way that is independent of the system catalog
layout but more comprehensive than the information schema.

To help implement the view, add a new internal function
pg_sequence_last_value() to return the last value of a sequence.  This
is kept separate from pg_sequence_parameters() to separate querying
run-time state from catalog-like information.

Reviewed-by: Andreas Karlsson <andreas@proxel.se>
This commit is contained in:
Peter Eisentraut
2016-11-18 12:00:00 -05:00
parent 8f91f323b4
commit 67dc4ccbb2
10 changed files with 233 additions and 10 deletions
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49
src/backend/commands/sequence.c
View File

@@ -1534,8 +1534,8 @@ pg_sequence_parameters(PG_FUNCTION_ARGS)
{
Oid relid = PG_GETARG_OID(0);
TupleDesc tupdesc;
Datum values[5];
bool isnull[5];
Datum values[6];
bool isnull[6];
SeqTable elm;
Relation seqrel;
Buffer buf;
@@ -1551,7 +1551,7 @@ pg_sequence_parameters(PG_FUNCTION_ARGS)
errmsg("permission denied for sequence %s",
RelationGetRelationName(seqrel))));
tupdesc = CreateTemplateTupleDesc(5, false);
tupdesc = CreateTemplateTupleDesc(6, false);
TupleDescInitEntry(tupdesc, (AttrNumber) 1, "start_value",
INT8OID, -1, 0);
TupleDescInitEntry(tupdesc, (AttrNumber) 2, "minimum_value",
@@ -1562,6 +1562,8 @@ pg_sequence_parameters(PG_FUNCTION_ARGS)
INT8OID, -1, 0);
TupleDescInitEntry(tupdesc, (AttrNumber) 5, "cycle_option",
BOOLOID, -1, 0);
TupleDescInitEntry(tupdesc, (AttrNumber) 6, "cache_size",
INT8OID, -1, 0);
BlessTupleDesc(tupdesc);
@@ -1574,6 +1576,7 @@ pg_sequence_parameters(PG_FUNCTION_ARGS)
values[2] = Int64GetDatum(seq->max_value);
values[3] = Int64GetDatum(seq->increment_by);
values[4] = BoolGetDatum(seq->is_cycled);
values[5] = Int64GetDatum(seq->cache_value);
UnlockReleaseBuffer(buf);
relation_close(seqrel, NoLock);
@@ -1581,6 +1584,46 @@ pg_sequence_parameters(PG_FUNCTION_ARGS)
return HeapTupleGetDatum(heap_form_tuple(tupdesc, values, isnull));
}
/*
* Return the last value from the sequence
*
* Note: This has a completely different meaning than lastval().
*/
Datum
pg_sequence_last_value(PG_FUNCTION_ARGS)
{
Oid relid = PG_GETARG_OID(0);
SeqTable elm;
Relation seqrel;
Buffer buf;
HeapTupleData seqtuple;
Form_pg_sequence seq;
bool is_called;
int64 result;
/* open and AccessShareLock sequence */
init_sequence(relid, &elm, &seqrel);
if (pg_class_aclcheck(relid, GetUserId(), ACL_SELECT | ACL_USAGE) != ACLCHECK_OK)
ereport(ERROR,
(errcode(ERRCODE_INSUFFICIENT_PRIVILEGE),
errmsg("permission denied for sequence %s",
RelationGetRelationName(seqrel))));
seq = read_seq_tuple(elm, seqrel, &buf, &seqtuple);
is_called = seq->is_called;
result = seq->last_value;
UnlockReleaseBuffer(buf);
relation_close(seqrel, NoLock);
if (is_called)
PG_RETURN_INT64(result);
else
PG_RETURN_NULL();
}
void
seq_redo(XLogReaderState *record)