1 files changed, 154 insertions, 0 deletions

diff --git a/src/backend/commands/sequence.c b/src/backend/commands/sequence.c
index c13cada3bf1..717bb0b2aa9 100644
--- a/src/backend/commands/sequence.c
+++ b/src/backend/commands/sequence.c
@@ -337,6 +337,160 @@ ResetSequence(Oid seq_relid)
 }
 
 /*
+ * Update the sequence state by modifying the existing sequence data row.
+ *
+ * This keeps the same relfilenode, so the behavior is non-transactional.
+ */
+static void
+SetSequence_non_transactional(Oid seqrelid, int64 last_value, int64 log_cnt, bool is_called)
+{
+	SeqTable	elm;
+	Relation	seqrel;
+	Buffer		buf;
+	HeapTupleData seqdatatuple;
+	Form_pg_sequence_data seq;
+
+	/* open and lock sequence */
+	init_sequence(seqrelid, &elm, &seqrel);
+
+	/* lock page' buffer and read tuple */
+	seq = read_seq_tuple(seqrel, &buf, &seqdatatuple);
+
+	/* check the comment above nextval_internal()'s equivalent call. */
+	if (RelationNeedsWAL(seqrel))
+	{
+		GetTopTransactionId();
+
+		if (XLogLogicalInfoActive())
+			GetCurrentTransactionId();
+	}
+
+	/* ready to change the on-disk (or really, in-buffer) tuple */
+	START_CRIT_SECTION();
+
+	seq->last_value = last_value;
+	seq->is_called = is_called;
+	seq->log_cnt = log_cnt;
+
+	MarkBufferDirty(buf);
+
+	/* XLOG stuff */
+	if (RelationNeedsWAL(seqrel))
+	{
+		xl_seq_rec	xlrec;
+		XLogRecPtr	recptr;
+		Page		page = BufferGetPage(buf);
+
+		XLogBeginInsert();
+		XLogRegisterBuffer(0, buf, REGBUF_WILL_INIT);
+
+		xlrec.node = seqrel->rd_node;
+		xlrec.created = false;
+
+		XLogRegisterData((char *) &xlrec, sizeof(xl_seq_rec));
+		XLogRegisterData((char *) seqdatatuple.t_data, seqdatatuple.t_len);
+
+		recptr = XLogInsert(RM_SEQ_ID, XLOG_SEQ_LOG);
+
+		PageSetLSN(page, recptr);
+	}
+
+	END_CRIT_SECTION();
+
+	UnlockReleaseBuffer(buf);
+
+	/* 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;
+
+	relation_close(seqrel, NoLock);
+}
+
+/*
+ * Update the sequence state by creating a new relfilenode.
+ *
+ * This creates a new relfilenode, to allow transactional behavior.
+ */
+static void
+SetSequence_transactional(Oid seq_relid, int64 last_value, int64 log_cnt, bool is_called)
+{
+	SeqTable	elm;
+	Relation	seqrel;
+	Buffer		buf;
+	HeapTupleData seqdatatuple;
+	Form_pg_sequence_data seq;
+	HeapTuple	tuple;
+
+	/* open and lock sequence */
+	init_sequence(seq_relid, &elm, &seqrel);
+
+	/* lock page' buffer and read tuple */
+	seq = read_seq_tuple(seqrel, &buf, &seqdatatuple);
+
+	/* Copy the existing sequence tuple. */
+	tuple = heap_copytuple(&seqdatatuple);
+
+	/* Now we're done with the old page */
+	UnlockReleaseBuffer(buf);
+
+	/*
+	 * Modify the copied tuple to update the sequence state (similar to what
+	 * ResetSequence does).
+	 */
+	seq = (Form_pg_sequence_data) GETSTRUCT(tuple);
+	seq->last_value = last_value;
+	seq->is_called = is_called;
+	seq->log_cnt = log_cnt;
+
+	/*
+	 * Create a new storage file for the sequence - this is needed for the
+	 * transactional behavior.
+	 */
+	RelationSetNewRelfilenode(seqrel, seqrel->rd_rel->relpersistence);
+
+	/*
+	 * Ensure sequence's relfrozenxid is at 0, since it won't contain any
+	 * unfrozen XIDs.  Same with relminmxid, since a sequence will never
+	 * contain multixacts.
+	 */
+	Assert(seqrel->rd_rel->relfrozenxid == InvalidTransactionId);
+	Assert(seqrel->rd_rel->relminmxid == InvalidMultiXactId);
+
+	/*
+	 * Insert the modified tuple into the new storage file. This does all the
+	 * necessary WAL-logging etc.
+	 */
+	fill_seq_with_data(seqrel, tuple);
+
+	/* 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;
+
+	relation_close(seqrel, NoLock);
+}
+
+/*
+ * Set a sequence to a specified internal state.
+ *
+ * The change is made transactionally, so that on failure of the current
+ * transaction, the sequence will be restored to its previous state.
+ * We do that by creating a whole new relfilenode for the sequence; so this
+ * works much like the rewriting forms of ALTER TABLE.
+ *
+ * Caller is assumed to have acquired AccessExclusiveLock on the sequence,
+ * which must not be released until end of transaction.  Caller is also
+ * responsible for permissions checking.
+ */
+void
+SetSequence(Oid seq_relid, bool transactional, int64 last_value, int64 log_cnt, bool is_called)
+{
+	if (transactional)
+		SetSequence_transactional(seq_relid, last_value, log_cnt, is_called);
+	else
+		SetSequence_non_transactional(seq_relid, last_value, log_cnt, is_called);
+}
+
+/*
  * Initialize a sequence's relation with the specified tuple as content
  */
 static void