From a9b6b01ee8a70d6abe8e5a56f18115c804fd10f4 Mon Sep 17 00:00:00 2001
From: Tom Lane <tgl@sss.pgh.pa.us>
Date: Tue, 24 Oct 2000 03:34:53 +0000
Subject: [PATCH] Reconsider page size for large objects: rather than stuffing
disk pages as full as possible, seems better to use a tuple size around
BLCKSZ/4 so that less space is wasted when a LO tuple is updated. Also, this
lets us use a logical page size that's an exact power of two, avoiding
partial-page writes when client is sending us stuff in power-of-2 buffer
chunks.
---
src/include/catalog/catversion.h | 4 ++--
src/include/storage/large_object.h | 19 ++++++++++++-------
2 files changed, 14 insertions(+), 9 deletions(-)
diff --git a/src/include/catalog/catversion.h b/src/include/catalog/catversion.h
index f6fd284f34d..56f515b662a 100644
--- a/src/include/catalog/catversion.h
+++ b/src/include/catalog/catversion.h
@@ -37,7 +37,7 @@
* Portions Copyright (c) 1996-2000, PostgreSQL, Inc
* Portions Copyright (c) 1994, Regents of the University of California
*
- * $Id: catversion.h,v 1.52 2000/10/24 01:38:41 tgl Exp $
+ * $Id: catversion.h,v 1.53 2000/10/24 03:34:15 tgl Exp $
*
*-------------------------------------------------------------------------
*/
@@ -53,6 +53,6 @@
*/
/* yyyymmddN */
-#define CATALOG_VERSION_NO 200010232
+#define CATALOG_VERSION_NO 200010233
#endif
diff --git a/src/include/storage/large_object.h b/src/include/storage/large_object.h
index 6bb0c4fcf2e..c7630124811 100644
--- a/src/include/storage/large_object.h
+++ b/src/include/storage/large_object.h
@@ -8,7 +8,7 @@
* Portions Copyright (c) 1996-2000, PostgreSQL, Inc
* Portions Copyright (c) 1994, Regents of the University of California
*
- * $Id: large_object.h,v 1.18 2000/10/24 01:38:43 tgl Exp $
+ * $Id: large_object.h,v 1.19 2000/10/24 03:34:53 tgl Exp $
*
*-------------------------------------------------------------------------
*/
@@ -47,13 +47,18 @@ typedef struct LargeObjectDesc {
/*
* Each "page" (tuple) of a large object can hold this much data
*
- * Calculation is max tuple size less tuple header, loid field (Oid),
- * pageno field (int32), and varlena header of data (int32). Note we
- * assume none of the fields will be NULL, hence no need for null bitmap.
+ * We could set this as high as BLCKSZ less some overhead, but it seems
+ * better to make it a smaller value, so that not as much space is used
+ * up when a page-tuple is updated. Note that the value is deliberately
+ * chosen large enough to trigger the tuple toaster, so that we will
+ * attempt to compress page tuples in-line. (But they won't be moved off
+ * unless the user creates a toast-table for pg_largeobject...)
+ *
+ * Also, it seems to be a smart move to make the page size be a power of 2,
+ * since clients will often be written to send data in power-of-2 blocks.
+ * This avoids unnecessary tuple updates caused by partial-page writes.
*/
-#define LOBLKSIZE (MaxTupleSize \
- - MAXALIGN(offsetof(HeapTupleHeaderData, t_bits)) \
- - sizeof(Oid) - sizeof(int32) * 2)
+#define LOBLKSIZE (BLCKSZ / 4)
/*
--
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