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Fix ALTER SEQUENCE so that it does not affect the value of currval() for

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the sequence.  Also, make setval() with is_called = false not affect the
currval state, either.  Per report from Kris Jurka that an implicit
ALTER SEQUENCE OWNED BY unexpectedly caused currval() to become valid.
Since this isn't 100% backwards compatible, it will go into HEAD only;
I'll put a more limited patch into 8.2.
This commit is contained in:
Tom Lane 2007-10-25 18:54:03 +00:00
parent dbe48765cd
commit 9ddfe034c7
3 changed files with 49 additions and 24 deletions
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23
doc/src/sgml/func.sgml
View File

@ -1,4 +1,4 @@
<!-- $PostgreSQL: pgsql/doc/src/sgml/func.sgml,v 1.404 2007/10/23 20:46:11 tgl Exp $ -->
<!-- $PostgreSQL: pgsql/doc/src/sgml/func.sgml,v 1.405 2007/10/25 18:54:03 tgl Exp $ -->
<chapter id="functions">
<title>Functions and Operators</title>
@ -8733,15 +8733,20 @@ nextval('foo'::text) <lineannotation><literal>foo</literal> is looked up at
<listitem>
<para>
Reset the sequence object's counter value. The two-parameter
form sets the sequence's <literal>last_value</literal> field to the specified
value and sets its <literal>is_called</literal> field to <literal>true</literal>,
meaning that the next <function>nextval</function> will advance the sequence
before returning a value. In the three-parameter form,
<literal>is_called</literal> can be set either <literal>true</literal> or
<literal>false</literal>. If it's set to <literal>false</literal>,
the next <function>nextval</function> will return exactly the specified
form sets the sequence's <literal>last_value</literal> field to the
specified value and sets its <literal>is_called</literal> field to
<literal>true</literal>, meaning that the next
<function>nextval</function> will advance the sequence before
returning a value. The value reported by <function>currval</> is
also set to the specified value. In the three-parameter form,
<literal>is_called</literal> can be set either <literal>true</literal>
or <literal>false</literal>. <literal>true</> has the same effect as
the two-parameter form. If it's set to <literal>false</literal>, the
next <function>nextval</function> will return exactly the specified
value, and sequence advancement commences with the following
<function>nextval</function>. For example,
<function>nextval</function>. Furthermore, the value reported by
<function>currval</> is not changed in this case (this is a change
from pre-8.3 behavior). For example,
<screen>
SELECT setval('foo', 42); <lineannotation>Next <function>nextval</> will return 43</lineannotation>

13
doc/src/sgml/ref/alter_sequence.sgml
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@ -1,5 +1,5 @@
<!--
$PostgreSQL: pgsql/doc/src/sgml/ref/alter_sequence.sgml,v 1.18 2007/10/03 16:48:43 tgl Exp $
$PostgreSQL: pgsql/doc/src/sgml/ref/alter_sequence.sgml,v 1.19 2007/10/25 18:54:03 tgl Exp $
PostgreSQL documentation
-->
@ -114,7 +114,10 @@ ALTER SEQUENCE <replaceable class="parameter">name</replaceable> SET SCHEMA <rep
<para>
The optional clause <literal>RESTART WITH <replaceable
class="parameter">start</replaceable></literal> changes the
current value of the sequence.
current value of the sequence. This is equivalent to calling the
<function>setval</> function with <literal>is_called</literal> =
<literal>false</>: the specified value will be returned by the
<emphasis>next</> call of <function>nextval</>.
</para>
</listitem>
</varlistentry>
@ -226,6 +229,12 @@ ALTER SEQUENCE <replaceable class="parameter">name</replaceable> SET SCHEMA <rep
immediately.
</para>
<para>
<command>ALTER SEQUENCE</command> does not affect the <function>currval</>
status for the sequence. (Before <productname>PostgreSQL</productname>
8.3, it sometimes did.)
</para>
<para>
Some variants of <command>ALTER TABLE</command> can be used with
sequences as well; for example, to rename a sequence it is also

37
src/backend/commands/sequence.c
View File

@ -8,7 +8,7 @@
*
*
* IDENTIFICATION
* $PostgreSQL: pgsql/src/backend/commands/sequence.c,v 1.146 2007/09/20 17:56:31 tgl Exp $
* $PostgreSQL: pgsql/src/backend/commands/sequence.c,v 1.147 2007/10/25 18:54:03 tgl Exp $
*
*-------------------------------------------------------------------------
*/
@ -65,10 +65,12 @@ typedef struct SeqTableData
struct SeqTableData *next; /* link to next SeqTable object */
Oid relid; /* pg_class OID of this sequence */
LocalTransactionId lxid; /* xact in which we last did a seq op */
bool last_valid; /* do we have a valid "last" value? */
int64 last; /* value last returned by nextval */
int64 cached; /* last value already cached for nextval */
/* if last != cached, we have not used up all the cached values */
int64 increment; /* copy of sequence's increment field */
/* note that increment is zero until we first do read_info() */
} SeqTableData;
typedef SeqTableData *SeqTable;
@ -336,14 +338,13 @@ AlterSequence(AlterSeqStmt *stmt)
/* Check and set new values */
init_params(stmt->options, false, &new, &owned_by);
/* Clear local cache so that we don't think we have cached numbers */
/* Note that we do not change the currval() state */
elm->cached = elm->last;
/* Now okay to update the on-disk tuple */
memcpy(seq, &new, sizeof(FormData_pg_sequence));
/* Clear local cache so that we don't think we have cached numbers */
elm->last = new.last_value; /* last returned number */
elm->cached = new.last_value; /* last cached number (forget cached
* values) */
START_CRIT_SECTION();
MarkBufferDirty(buf);
@ -443,9 +444,11 @@ nextval_internal(Oid relid)
if (elm->last != elm->cached) /* some numbers were cached */
{
last_used_seq = elm;
Assert(elm->last_valid);
Assert(elm->increment != 0);
elm->last += elm->increment;
relation_close(seqrel, NoLock);
last_used_seq = elm;
return elm->last;
}
@ -564,6 +567,7 @@ nextval_internal(Oid relid)
/* save info in local cache */
elm->last = result; /* last returned number */
elm->cached = last; /* last fetched number */
elm->last_valid = true;
last_used_seq = elm;
@ -633,7 +637,7 @@ currval_oid(PG_FUNCTION_ARGS)
errmsg("permission denied for sequence %s",
RelationGetRelationName(seqrel))));
if (elm->increment == 0) /* nextval/read_info were not called */
if (!elm->last_valid)
ereport(ERROR,
(errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
errmsg("currval of sequence \"%s\" is not yet defined in this session",
@ -668,7 +672,7 @@ lastval(PG_FUNCTION_ARGS)
seqrel = open_share_lock(last_used_seq);
/* nextval() must have already been called for this sequence */
Assert(last_used_seq->increment != 0);
Assert(last_used_seq->last_valid);
if (pg_class_aclcheck(last_used_seq->relid, GetUserId(), ACL_SELECT) != ACLCHECK_OK &&
pg_class_aclcheck(last_used_seq->relid, GetUserId(), ACL_USAGE) != ACLCHECK_OK)
@ -732,9 +736,15 @@ do_setval(Oid relid, int64 next, bool iscalled)
bufm, bufx)));
}
/* save info in local cache */
elm->last = next; /* last returned number */
elm->cached = next; /* last cached number (forget cached values) */
/* Set the currval() state only if iscalled = true */
if (iscalled)
{
elm->last = next; /* last returned number */
elm->last_valid = true;
}
/* In any case, forget any future cached numbers */
elm->cached = elm->last;
START_CRIT_SECTION();
@ -893,7 +903,7 @@ init_sequence(Oid relid, SeqTable *p_elm, Relation *p_rel)
errmsg("out of memory")));
elm->relid = relid;
elm->lxid = InvalidLocalTransactionId;
/* increment is set to 0 until we do read_info (see currval) */
elm->last_valid = false;
elm->last = elm->cached = elm->increment = 0;
elm->next = seqtab;
seqtab = elm;
@ -941,6 +951,7 @@ read_info(SeqTable elm, Relation rel, Buffer *buf)
seq = (Form_pg_sequence) GETSTRUCT(&tuple);
/* this is a handy place to update our copy of the increment */
elm->increment = seq->increment_by;
return seq;