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

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.

diff --git a/doc/src/sgml/func.sgml b/doc/src/sgml/func.sgml
index c9d6653..5feb572 100644 (file)
--- a/doc/src/sgml/func.sgml
+++ b/doc/src/sgml/func.sgml
@@ -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>

diff --git a/doc/src/sgml/ref/alter_sequence.sgml b/doc/src/sgml/ref/alter_sequence.sgml
index b515ae4..3c982ee 100644 (file)
--- a/doc/src/sgml/ref/alter_sequence.sgml
+++ b/doc/src/sgml/ref/alter_sequence.sgml
@@ -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>
@@ -227,6 +230,12 @@ ALTER SEQUENCE <replaceable class="parameter">name</replaceable> SET SCHEMA <rep
   </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
    possible to use <command>ALTER TABLE RENAME</command>.

diff --git a/src/backend/commands/sequence.c b/src/backend/commands/sequence.c
index 25d1e23..619e289 100644 (file)
--- a/src/backend/commands/sequence.c
+++ b/src/backend/commands/sequence.c
@@ -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;