From ce66e24081ead2cb42b02f007039287947d0cca6 Mon Sep 17 00:00:00 2001
From: Michael Paquier <michael@otacoo.com>
Date: Fri, 4 Jul 2014 13:34:47 +0900
Subject: [PATCH 1/3] Move SEQ_MAGIC and sequence page opaque data to
 sequence.h

This can allow a backend process to detect if a page is being used
for a sequence.
---
 src/backend/commands/sequence.c | 34 ++++++++++++----------------------
 src/include/commands/sequence.h | 13 +++++++++++++
 2 files changed, 25 insertions(+), 22 deletions(-)

diff --git a/src/backend/commands/sequence.c b/src/backend/commands/sequence.c
index e608420..802aac7 100644
--- a/src/backend/commands/sequence.c
+++ b/src/backend/commands/sequence.c
@@ -46,16 +46,6 @@
 #define SEQ_LOG_VALS	32
 
 /*
- * The "special area" of a sequence's buffer page looks like this.
- */
-#define SEQ_MAGIC	  0x1717
-
-typedef struct sequence_magic
-{
-	uint32		magic;
-} sequence_magic;
-
-/*
  * We store a SeqTable item for every sequence we have touched in the current
  * session.  This is needed to hold onto nextval/currval state.  (We can't
  * rely on the relcache, since it's only, well, a cache, and may decide to
@@ -306,7 +296,7 @@ fill_seq_with_data(Relation rel, HeapTuple tuple)
 {
 	Buffer		buf;
 	Page		page;
-	sequence_magic *sm;
+	SequencePageOpaqueData *sm;
 	OffsetNumber offnum;
 
 	/* Initialize first page of relation with special magic number */
@@ -316,9 +306,9 @@ fill_seq_with_data(Relation rel, HeapTuple tuple)
 
 	page = BufferGetPage(buf);
 
-	PageInit(page, BufferGetPageSize(buf), sizeof(sequence_magic));
-	sm = (sequence_magic *) PageGetSpecialPointer(page);
-	sm->magic = SEQ_MAGIC;
+	PageInit(page, BufferGetPageSize(buf), sizeof(SequencePageOpaqueData));
+	sm = (SequencePageOpaqueData *) PageGetSpecialPointer(page);
+	sm->seq_page_id = SEQ_MAGIC;
 
 	/* Now insert sequence tuple */
 
@@ -1066,18 +1056,18 @@ read_seq_tuple(SeqTable elm, Relation rel, Buffer *buf, HeapTuple seqtuple)
 {
 	Page		page;
 	ItemId		lp;
-	sequence_magic *sm;
+	SequencePageOpaqueData *sm;
 	Form_pg_sequence seq;
 
 	*buf = ReadBuffer(rel, 0);
 	LockBuffer(*buf, BUFFER_LOCK_EXCLUSIVE);
 
 	page = BufferGetPage(*buf);
-	sm = (sequence_magic *) PageGetSpecialPointer(page);
+	sm = (SequencePageOpaqueData *) PageGetSpecialPointer(page);
 
-	if (sm->magic != SEQ_MAGIC)
+	if (sm->seq_page_id != SEQ_MAGIC)
 		elog(ERROR, "bad magic number in sequence \"%s\": %08X",
-			 RelationGetRelationName(rel), sm->magic);
+			 RelationGetRelationName(rel), sm->seq_page_id);
 
 	lp = PageGetItemId(page, FirstOffsetNumber);
 	Assert(ItemIdIsNormal(lp));
@@ -1541,7 +1531,7 @@ seq_redo(XLogRecPtr lsn, XLogRecord *record)
 	char	   *item;
 	Size		itemsz;
 	xl_seq_rec *xlrec = (xl_seq_rec *) XLogRecGetData(record);
-	sequence_magic *sm;
+	SequencePageOpaqueData *sm;
 
 	/* Backup blocks are not used in seq records */
 	Assert(!(record->xl_info & XLR_BKP_BLOCK_MASK));
@@ -1564,9 +1554,9 @@ seq_redo(XLogRecPtr lsn, XLogRecord *record)
 	 */
 	localpage = (Page) palloc(BufferGetPageSize(buffer));
 
-	PageInit(localpage, BufferGetPageSize(buffer), sizeof(sequence_magic));
-	sm = (sequence_magic *) PageGetSpecialPointer(localpage);
-	sm->magic = SEQ_MAGIC;
+	PageInit(localpage, BufferGetPageSize(buffer), sizeof(SequencePageOpaqueData));
+	sm = (SequencePageOpaqueData *) PageGetSpecialPointer(localpage);
+	sm->seq_page_id = SEQ_MAGIC;
 
 	item = (char *) xlrec + sizeof(xl_seq_rec);
 	itemsz = record->xl_len - sizeof(xl_seq_rec);
diff --git a/src/include/commands/sequence.h b/src/include/commands/sequence.h
index 8819c00..2455878 100644
--- a/src/include/commands/sequence.h
+++ b/src/include/commands/sequence.h
@@ -18,6 +18,19 @@
 #include "nodes/parsenodes.h"
 #include "storage/relfilenode.h"
 
+/*
+ * Page opaque data in a sequence page
+ */
+typedef struct SequencePageOpaqueData
+{
+	uint32 seq_page_id;
+} SequencePageOpaqueData;
+
+/*
+ * This page ID is for the conveniende to be able to identify if a page
+ * is being used by a sequence.
+ */
+#define SEQ_MAGIC		0x1717
 
 typedef struct FormData_pg_sequence
 {
-- 
2.0.1