From ca7c8168de76459380577eda56a3ed09b4f6195c Mon Sep 17 00:00:00 2001
From: Tom Lane <tgl@sss.pgh.pa.us>
Date: Wed, 22 Jul 2009 01:21:22 +0000
Subject: [PATCH] Tweak TOAST code so that columns marked with MAIN storage
strategy are not forced out-of-line unless that is necessary to make the row
fit on a page. Previously, they were forced out-of-line if needed to get the
row down to the default target size (1/4th page).
Kevin Grittner
---
doc/src/sgml/storage.sgml | 4 +--
src/backend/access/heap/tuptoaster.c | 8 ++++--
src/include/access/tuptoaster.h | 39 ++++++++++++++++++----------
3 files changed, 33 insertions(+), 18 deletions(-)
diff --git a/doc/src/sgml/storage.sgml b/doc/src/sgml/storage.sgml
index ee7f814ea89..fcdbd0ee36f 100644
--- a/doc/src/sgml/storage.sgml
+++ b/doc/src/sgml/storage.sgml
@@ -1,4 +1,4 @@
-<!-- $PostgreSQL: pgsql/doc/src/sgml/storage.sgml,v 1.29 2009/06/17 21:58:49 tgl Exp $ -->
+<!-- $PostgreSQL: pgsql/doc/src/sgml/storage.sgml,v 1.30 2009/07/22 01:21:22 tgl Exp $ -->
<chapter id="storage">
@@ -347,7 +347,7 @@ The <acronym>TOAST</> code recognizes four different strategies for storing
<literal>MAIN</literal> allows compression but not out-of-line
storage. (Actually, out-of-line storage will still be performed
for such columns, but only as a last resort when there is no other
- way to make the row small enough.)
+ way to make the row small enough to fit on a page.)
</para>
</listitem>
</itemizedlist>
diff --git a/src/backend/access/heap/tuptoaster.c b/src/backend/access/heap/tuptoaster.c
index a3203085b7a..781bfd2e486 100644
--- a/src/backend/access/heap/tuptoaster.c
+++ b/src/backend/access/heap/tuptoaster.c
@@ -8,7 +8,7 @@
*
*
* IDENTIFICATION
- * $PostgreSQL: pgsql/src/backend/access/heap/tuptoaster.c,v 1.93 2009/06/11 14:48:54 momjian Exp $
+ * $PostgreSQL: pgsql/src/backend/access/heap/tuptoaster.c,v 1.94 2009/07/22 01:21:22 tgl Exp $
*
*
* INTERFACE ROUTINES
@@ -796,8 +796,12 @@ toast_insert_or_update(Relation rel, HeapTuple newtup, HeapTuple oldtup,
}
/*
- * Finally we store attributes of type 'm' external, if possible.
+ * Finally we store attributes of type 'm' externally. At this point
+ * we increase the target tuple size, so that 'm' attributes aren't
+ * stored externally unless really necessary.
*/
+ maxDataLen = TOAST_TUPLE_TARGET_MAIN - hoff;
+
while (heap_compute_data_size(tupleDesc,
toast_values, toast_isnull) > maxDataLen &&
rel->rd_rel->reltoastrelid != InvalidOid)
diff --git a/src/include/access/tuptoaster.h b/src/include/access/tuptoaster.h
index db2f7e57607..f8dd7f82f5b 100644
--- a/src/include/access/tuptoaster.h
+++ b/src/include/access/tuptoaster.h
@@ -6,7 +6,7 @@
*
* Copyright (c) 2000-2009, PostgreSQL Global Development Group
*
- * $PostgreSQL: pgsql/src/include/access/tuptoaster.h,v 1.43 2009/01/01 17:23:56 momjian Exp $
+ * $PostgreSQL: pgsql/src/include/access/tuptoaster.h,v 1.44 2009/07/22 01:21:22 tgl Exp $
*
*-------------------------------------------------------------------------
*/
@@ -24,20 +24,26 @@
#define TOAST_INDEX_HACK
+/*
+ * Find the maximum size of a tuple if there are to be N tuples per page.
+ */
+#define MaximumBytesPerTuple(tuplesPerPage) \
+ MAXALIGN_DOWN((BLCKSZ - \
+ MAXALIGN(SizeOfPageHeaderData + (tuplesPerPage) * sizeof(ItemIdData))) \
+ / (tuplesPerPage))
+
/*
* These symbols control toaster activation. If a tuple is larger than
* TOAST_TUPLE_THRESHOLD, we will try to toast it down to no more than
- * TOAST_TUPLE_TARGET bytes. Both numbers include all tuple header overhead
- * and between-fields alignment padding, but we do *not* consider any
- * end-of-tuple alignment padding; hence the values can be compared directly
- * to a tuple's t_len field.
+ * TOAST_TUPLE_TARGET bytes through compressing compressible fields and
+ * moving EXTENDED and EXTERNAL data out-of-line.
*
* The numbers need not be the same, though they currently are. It doesn't
* make sense for TARGET to exceed THRESHOLD, but it could be useful to make
* it be smaller.
*
* Currently we choose both values to match the largest tuple size for which
- * TOAST_TUPLES_PER_PAGE tuples can fit on a disk page.
+ * TOAST_TUPLES_PER_PAGE tuples can fit on a heap page.
*
* XXX while these can be modified without initdb, some thought needs to be
* given to needs_toast_table() in toasting.c before unleashing random
@@ -46,13 +52,21 @@
*/
#define TOAST_TUPLES_PER_PAGE 4
-#define TOAST_TUPLE_THRESHOLD \
- MAXALIGN_DOWN((BLCKSZ - \
- MAXALIGN(SizeOfPageHeaderData + TOAST_TUPLES_PER_PAGE * sizeof(ItemIdData))) \
- / TOAST_TUPLES_PER_PAGE)
+#define TOAST_TUPLE_THRESHOLD MaximumBytesPerTuple(TOAST_TUPLES_PER_PAGE)
#define TOAST_TUPLE_TARGET TOAST_TUPLE_THRESHOLD
+/*
+ * The code will also consider moving MAIN data out-of-line, but only as a
+ * last resort if the previous steps haven't reached the target tuple size.
+ * In this phase we use a different target size, currently equal to the
+ * largest tuple that will fit on a heap page. This is reasonable since
+ * the user has told us to keep the data in-line if at all possible.
+ */
+#define TOAST_TUPLES_PER_PAGE_MAIN 1
+
+#define TOAST_TUPLE_TARGET_MAIN MaximumBytesPerTuple(TOAST_TUPLES_PER_PAGE_MAIN)
+
/*
* If an index value is larger than TOAST_INDEX_TARGET, we will try to
* compress it (we can't move it out-of-line, however). Note that this
@@ -72,10 +86,7 @@
*/
#define EXTERN_TUPLES_PER_PAGE 4 /* tweak only this */
-#define EXTERN_TUPLE_MAX_SIZE \
- MAXALIGN_DOWN((BLCKSZ - \
- MAXALIGN(SizeOfPageHeaderData + EXTERN_TUPLES_PER_PAGE * sizeof(ItemIdData))) \
- / EXTERN_TUPLES_PER_PAGE)
+#define EXTERN_TUPLE_MAX_SIZE MaximumBytesPerTuple(EXTERN_TUPLES_PER_PAGE)
#define TOAST_MAX_CHUNK_SIZE \
(EXTERN_TUPLE_MAX_SIZE - \
--
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