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Code review for btree page split WAL reduction patch. Make it actually work

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(original code *always* created a full-page image for the left page, thus
leaving the intended savings unrealized), avoid risk of not having enough room
on the page during xlog restore, squeeze out another couple bytes in the xlog
record, clean up neglected comments.
This commit is contained in:
Tom Lane
2007-04-11 20:47:38 +00:00
parent f7424b0d4b
commit 226a100568
4 changed files with 166 additions and 126 deletions
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41
src/include/access/nbtree.h
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@@ -7,7 +7,7 @@
* Portions Copyright (c) 1996-2007, PostgreSQL Global Development Group
* Portions Copyright (c) 1994, Regents of the University of California
*
* $PostgreSQL: pgsql/src/include/access/nbtree.h,v 1.112 2007/04/09 22:04:08 tgl Exp $
* $PostgreSQL: pgsql/src/include/access/nbtree.h,v 1.113 2007/04/11 20:47:38 tgl Exp $
*
*-------------------------------------------------------------------------
*/
@@ -260,17 +260,17 @@ typedef struct xl_btree_insert
#define SizeOfBtreeInsert (offsetof(xl_btreetid, tid) + SizeOfIptrData)
/*
* On insert with split we save items of both left and right siblings
* and restore content of both pages from log record. This way takes less
* xlog space than the normal approach, because if we did it standardly,
* On insert with split, we save all the items going into the right sibling
* so that we can restore it completely from the log record. This way takes
* less xlog space than the normal approach, because if we did it standardly,
* XLogInsert would almost always think the right page is new and store its
* whole page image.
* whole page image. The left page, however, is handled in the normal
* incremental-update fashion.
*
* Note: the four XLOG_BTREE_SPLIT xl_info codes all use this data record.
* The _L and _R variants indicate whether the inserted tuple went into the
* left or right split page (and thus, whether newitemoff and the new item
* are stored or not.
* page of the split pair). The _ROOT variants indicate that we are splitting
* are stored or not). The _ROOT variants indicate that we are splitting
* the root page, and thus that a newroot record rather than an insert or
* split record should follow. Note that a split record never carries a
* metapage update --- we'll do that in the parent-level update.
@@ -278,20 +278,25 @@ typedef struct xl_btree_insert
typedef struct xl_btree_split
{
RelFileNode node;
BlockNumber leftsib; /* orig page / new left page */
BlockNumber rightsib; /* new right page */
OffsetNumber firstright; /* first item stored on right page */
BlockNumber rnext; /* next/right block pointer */
uint32 level; /* tree level of page being split */
BlockNumber leftsib; /* orig page / new left page */
BlockNumber rightsib; /* new right page */
BlockNumber rnext; /* next block (orig page's rightlink) */
uint32 level; /* tree level of page being split */
OffsetNumber firstright; /* first item moved to right page */
/* BlockIdData downlink follows if level > 0 */
/* OffsetNumber newitemoff follows in the _L variants. */
/* New item follows in the _L variants */
/* RIGHT PAGES TUPLES FOLLOW AT THE END */
/*
* If level > 0, BlockIdData downlink follows. (We use BlockIdData
* rather than BlockNumber for alignment reasons: SizeOfBtreeSplit
* is only 16-bit aligned.)
*
* In the _L variants, next are OffsetNumber newitemoff and the new item.
* (In the _R variants, the new item is one of the right page's tuples.)
*
* Last are the right page's tuples in the form used by _bt_restore_page.
*/
} xl_btree_split;
#define SizeOfBtreeSplit (offsetof(xl_btree_split, level) + sizeof(uint32))
#define SizeOfBtreeSplit (offsetof(xl_btree_split, firstright) + sizeof(OffsetNumber))
/*
* This is what we need to know about delete of individual leaf index tuples.