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Improve handling of prune/no-prune decisions by storing a page's oldest
unpruned XMAX in its header. At the cost of 4 bytes per page, this keeps us from performing heap_page_prune when there's no chance of pruning anything. Seems to be necessary per Heikki's preliminary performance testing.
This commit is contained in:
Tom Lane
parent
386a5d4268
commit
cc59049daf
@ -23,14 +23,14 @@ only by superusers.
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A page image obtained with get_raw_page should be passed as argument:
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test=# SELECT * FROM page_header(get_raw_page('pg_class',0));
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lsn | tli | flags | lower | upper | special | pagesize | version
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----------+-----+-------+-------+-------+---------+----------+---------
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0/3C5614 | 1 | 1 | 216 | 256 | 8192 | 8192 | 4
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regression=# SELECT * FROM page_header(get_raw_page('pg_class',0));
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lsn | tli | flags | lower | upper | special | pagesize | version | prune_xid
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-----------+-----+-------+-------+-------+---------+----------+---------+-----------
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0/24A1B50 | 1 | 1 | 232 | 368 | 8192 | 8192 | 4 | 0
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(1 row)
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The returned columns correspond to the fields in the PageHeaderData-struct,
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see src/include/storage/bufpage.h for more details.
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The returned columns correspond to the fields in the PageHeaderData struct.
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See src/include/storage/bufpage.h for details.
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heap_page_items
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---------------
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@ -20,7 +20,8 @@ CREATE OR REPLACE FUNCTION page_header(IN page bytea,
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OUT upper smallint,
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OUT special smallint,
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OUT pagesize smallint,
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OUT version smallint)
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OUT version smallint,
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OUT prune_xid xid)
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AS 'MODULE_PATHNAME', 'page_header'
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LANGUAGE C STRICT;
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@ -8,7 +8,7 @@
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* Copyright (c) 2007, PostgreSQL Global Development Group
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*
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* IDENTIFICATION
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* $PostgreSQL: pgsql/contrib/pageinspect/rawpage.c,v 1.1 2007/05/17 19:11:24 momjian Exp $
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* $PostgreSQL: pgsql/contrib/pageinspect/rawpage.c,v 1.2 2007/09/21 21:25:42 tgl Exp $
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*
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*-------------------------------------------------------------------------
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*/
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@ -110,8 +110,8 @@ page_header(PG_FUNCTION_ARGS)
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Datum result;
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HeapTuple tuple;
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Datum values[8];
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bool nulls[8];
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Datum values[9];
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bool nulls[9];
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PageHeader page;
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XLogRecPtr lsn;
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@ -152,6 +152,7 @@ page_header(PG_FUNCTION_ARGS)
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values[5] = UInt16GetDatum(page->pd_special);
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values[6] = UInt16GetDatum(PageGetPageSize(page));
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values[7] = UInt16GetDatum(PageGetPageLayoutVersion(page));
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values[8] = TransactionIdGetDatum(page->pd_prune_xid);
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/* Build and return the tuple. */
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@ -1,4 +1,4 @@
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<!-- $PostgreSQL: pgsql/doc/src/sgml/storage.sgml,v 1.18 2007/06/03 17:05:53 tgl Exp $ -->
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<!-- $PostgreSQL: pgsql/doc/src/sgml/storage.sgml,v 1.19 2007/09/21 21:25:42 tgl Exp $ -->
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<chapter id="storage">
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@ -416,7 +416,7 @@ Item
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<row>
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<entry>PageHeaderData</entry>
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<entry>20 bytes long. Contains general information about the page, including
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<entry>24 bytes long. Contains general information about the page, including
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free space pointers.</entry>
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</row>
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@ -449,7 +449,7 @@ data. Empty in ordinary tables.</entry>
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<para>
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The first 20 bytes of each page consists of a page header
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The first 24 bytes of each page consists of a page header
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(PageHeaderData). Its format is detailed in <xref
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linkend="pageheaderdata-table">. The first two fields track the most
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recent WAL entry related to this page. Next is a 2-byte field
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@ -459,7 +459,7 @@ data. Empty in ordinary tables.</entry>
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from the page start to the start
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of unallocated space, to the end of unallocated space, and to the start of
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the special space.
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The last 2 bytes of the page header,
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The next 2 bytes of the page header,
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<structfield>pd_pagesize_version</structfield>, store both the page size
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and a version indicator. Beginning with
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<productname>PostgreSQL</productname> 8.3 the version number is 4;
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@ -471,6 +471,8 @@ data. Empty in ordinary tables.</entry>
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versions, but the layout of heap row headers has.) The page size
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is basically only present as a cross-check; there is no support for having
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more than one page size in an installation.
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The last field is a hint that shows whether pruning the page is likely
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to be profitable: it tracks the oldest un-pruned XMAX on the page.
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</para>
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@ -530,6 +532,12 @@ data. Empty in ordinary tables.</entry>
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<entry>2 bytes</entry>
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<entry>Page size and layout version number information</entry>
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</row>
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<row>
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<entry>pd_prune_xid</entry>
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<entry>TransactionId</entry>
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<entry>4 bytes</entry>
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<entry>Oldest unpruned XMAX on page, or zero if none</entry>
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</row>
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</tbody>
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</tgroup>
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</table>
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@ -1,4 +1,4 @@
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$PostgreSQL: pgsql/src/backend/access/heap/README.HOT,v 1.1 2007/09/20 17:56:30 tgl Exp $
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$PostgreSQL: pgsql/src/backend/access/heap/README.HOT,v 1.2 2007/09/21 21:25:42 tgl Exp $
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Heap Only Tuples (HOT)
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@ -233,8 +233,8 @@ subsequent index searches. However it is unclear that this gain is
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large enough to accept any extra maintenance burden for.
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The currently planned heuristic is to prune and defrag when first accessing
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a page that potentially has prunable tuples (flagged by the PD_PRUNABLE
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page hint bit) and that either has free space less than MAX(fillfactor
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a page that potentially has prunable tuples (as flagged by the pd_prune_xid
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page hint field) and that either has free space less than MAX(fillfactor
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target free space, BLCKSZ/10) *or* has recently had an UPDATE fail to
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find enough free space to store an updated tuple version. (These rules
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are subject to change.)
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@ -8,7 +8,7 @@
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*
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*
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* IDENTIFICATION
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* $PostgreSQL: pgsql/src/backend/access/heap/heapam.c,v 1.241 2007/09/20 17:56:30 tgl Exp $
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* $PostgreSQL: pgsql/src/backend/access/heap/heapam.c,v 1.242 2007/09/21 21:25:42 tgl Exp $
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*
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*
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* INTERFACE ROUTINES
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@ -2068,11 +2068,12 @@ l1:
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/*
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* If this transaction commits, the tuple will become DEAD sooner or
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* later. Set hint bit that this page is a candidate for pruning. If
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* the transaction finally aborts, the subsequent page pruning will be
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* a no-op and the hint will be cleared.
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* later. Set flag that this page is a candidate for pruning once our xid
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* falls below the OldestXmin horizon. If the transaction finally aborts,
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* the subsequent page pruning will be a no-op and the hint will be
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* cleared.
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*/
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PageSetPrunable((Page) dp);
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PageSetPrunable(dp, xid);
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/* store transaction information of xact deleting the tuple */
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tp.t_data->t_infomask &= ~(HEAP_XMAX_COMMITTED |
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@ -2571,16 +2572,17 @@ l2:
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/*
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* If this transaction commits, the old tuple will become DEAD sooner or
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* later. Set hint bit that this page is a candidate for pruning. If
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* the transaction finally aborts, the subsequent page pruning will be
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* a no-op and the hint will be cleared.
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* later. Set flag that this page is a candidate for pruning once our xid
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* falls below the OldestXmin horizon. If the transaction finally aborts,
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* the subsequent page pruning will be a no-op and the hint will be
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* cleared.
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*
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* XXX Should we set hint on newbuf as well? If the transaction
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* aborts, there would be a prunable tuple in the newbuf; but for now
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* we choose not to optimize for aborts. Note that heap_xlog_update
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* must be kept in sync if this changes.
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* must be kept in sync if this decision changes.
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*/
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PageSetPrunable(dp);
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PageSetPrunable(dp, xid);
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if (use_hot_update)
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{
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@ -4108,7 +4110,7 @@ heap_xlog_delete(XLogRecPtr lsn, XLogRecord *record)
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HeapTupleHeaderSetCmax(htup, FirstCommandId, false);
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/* Mark the page as a candidate for pruning */
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PageSetPrunable(page);
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PageSetPrunable(page, record->xl_xid);
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/* Make sure there is no forward chain link in t_ctid */
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htup->t_ctid = xlrec->target.tid;
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@ -4284,7 +4286,7 @@ heap_xlog_update(XLogRecPtr lsn, XLogRecord *record, bool move, bool hot_update)
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}
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/* Mark the page as a candidate for pruning */
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PageSetPrunable(page);
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PageSetPrunable(page, record->xl_xid);
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/*
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* this test is ugly, but necessary to avoid thinking that insert change
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@ -8,7 +8,7 @@
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*
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*
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* IDENTIFICATION
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* $PostgreSQL: pgsql/src/backend/access/heap/pruneheap.c,v 1.1 2007/09/20 17:56:30 tgl Exp $
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* $PostgreSQL: pgsql/src/backend/access/heap/pruneheap.c,v 1.2 2007/09/21 21:25:42 tgl Exp $
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*
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*-------------------------------------------------------------------------
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*/
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@ -63,9 +63,10 @@ heap_page_prune_opt(Relation relation, Buffer buffer, TransactionId OldestXmin)
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/*
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* Let's see if we really need pruning.
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*
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* Forget it if page is not hinted to contain something prunable
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* Forget it if page is not hinted to contain something prunable that's
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* older than OldestXmin.
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*/
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if (!PageIsPrunable(dp))
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if (!PageIsPrunable(dp, OldestXmin))
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return;
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/*
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@ -93,6 +94,8 @@ heap_page_prune_opt(Relation relation, Buffer buffer, TransactionId OldestXmin)
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/*
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* Now that we have buffer lock, get accurate information about the
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* page's free space, and recheck the heuristic about whether to prune.
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* (We needn't recheck PageIsPrunable, since no one else could have
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* pruned while we hold pin.)
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*/
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if (PageIsFull(dp) || PageGetHeapFreeSpace((Page) dp) < minfree)
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{
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@ -147,7 +150,7 @@ heap_page_prune(Relation relation, Buffer buffer, TransactionId OldestXmin,
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START_CRIT_SECTION();
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/*
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* Mark the page as clear of prunable tuples. If we find a tuple which
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* Mark the page as clear of prunable tuples. If we find a tuple which
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* may soon become prunable, we shall set the hint again. Also clear
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* the "page is full" flag, since there's no point in repeating the
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* prune/defrag process until something else happens to the page.
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@ -203,6 +206,14 @@ heap_page_prune(Relation relation, Buffer buffer, TransactionId OldestXmin,
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PageSetLSN(BufferGetPage(buffer), recptr);
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}
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}
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else
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{
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/*
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* If we didn't prune anything, we have nonetheless updated the
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* pd_prune_xid field; treat this as a non-WAL-logged hint.
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*/
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SetBufferCommitInfoNeedsSave(buffer);
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}
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END_CRIT_SECTION();
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@ -392,18 +403,18 @@ heap_prune_chain(Relation relation, Buffer buffer, OffsetNumber rootoffnum,
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case HEAPTUPLE_RECENTLY_DEAD:
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recent_dead = true;
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/*
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* This tuple may soon become DEAD. Re-set the hint bit so
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* This tuple may soon become DEAD. Update the hint field so
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* that the page is reconsidered for pruning in future.
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*/
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PageSetPrunable(dp);
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PageSetPrunable(dp, HeapTupleHeaderGetXmax(htup));
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break;
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case HEAPTUPLE_DELETE_IN_PROGRESS:
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/*
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* This tuple may soon become DEAD. Re-set the hint bit so
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* This tuple may soon become DEAD. Update the hint field so
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* that the page is reconsidered for pruning in future.
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*/
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PageSetPrunable(dp);
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PageSetPrunable(dp, HeapTupleHeaderGetXmax(htup));
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break;
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case HEAPTUPLE_LIVE:
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@ -8,7 +8,7 @@
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*
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*
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* IDENTIFICATION
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* $PostgreSQL: pgsql/src/backend/storage/page/bufpage.c,v 1.74 2007/09/20 17:56:31 tgl Exp $
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* $PostgreSQL: pgsql/src/backend/storage/page/bufpage.c,v 1.75 2007/09/21 21:25:42 tgl Exp $
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*
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*-------------------------------------------------------------------------
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*/
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@ -40,11 +40,12 @@ PageInit(Page page, Size pageSize, Size specialSize)
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/* Make sure all fields of page are zero, as well as unused space */
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MemSet(p, 0, pageSize);
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/* p->pd_flags = 0; done by above MemSet */
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/* p->pd_flags = 0; done by above MemSet */
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p->pd_lower = SizeOfPageHeaderData;
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p->pd_upper = pageSize - specialSize;
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p->pd_special = pageSize - specialSize;
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PageSetPageSizeAndVersion(page, pageSize, PG_PAGE_LAYOUT_VERSION);
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/* p->pd_prune_xid = InvalidTransactionId; done by above MemSet */
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}
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@ -37,7 +37,7 @@
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* Portions Copyright (c) 1996-2007, PostgreSQL Global Development Group
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* Portions Copyright (c) 1994, Regents of the University of California
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*
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* $PostgreSQL: pgsql/src/include/catalog/catversion.h,v 1.426 2007/09/20 17:56:32 tgl Exp $
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* $PostgreSQL: pgsql/src/include/catalog/catversion.h,v 1.427 2007/09/21 21:25:42 tgl Exp $
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*
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*-------------------------------------------------------------------------
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*/
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@ -53,6 +53,6 @@
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*/
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/* yyyymmddN */
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#define CATALOG_VERSION_NO 200709201
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#define CATALOG_VERSION_NO 200709211
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#endif
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@ -7,7 +7,7 @@
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* Portions Copyright (c) 1996-2007, PostgreSQL Global Development Group
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* Portions Copyright (c) 1994, Regents of the University of California
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*
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* $PostgreSQL: pgsql/src/include/storage/bufpage.h,v 1.74 2007/09/20 17:56:32 tgl Exp $
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* $PostgreSQL: pgsql/src/include/storage/bufpage.h,v 1.75 2007/09/21 21:25:42 tgl Exp $
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*
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*-------------------------------------------------------------------------
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*/
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@ -48,7 +48,7 @@
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*
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* EXCEPTIONS:
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*
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* obviously, a page is not formatted before it is initialized with by
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* obviously, a page is not formatted before it is initialized by
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* a call to PageInit.
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*
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* NOTES:
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@ -95,6 +95,7 @@ typedef uint16 LocationIndex;
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* pd_upper - offset to end of free space.
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* pd_special - offset to start of special space.
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* pd_pagesize_version - size in bytes and page layout version number.
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* pd_prune_xid - oldest XID among potentially prunable tuples on page.
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*
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* The LSN is used by the buffer manager to enforce the basic rule of WAL:
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* "thou shalt write xlog before data". A dirty buffer cannot be dumped
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@ -103,6 +104,9 @@ typedef uint16 LocationIndex;
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* purposes (it is not clear that this is actually necessary, but it seems
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* like a good idea).
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*
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* pd_prune_xid is a hint field that helps determine whether pruning will be
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* useful. It is currently unused in index pages.
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*
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* The page version number and page size are packed together into a single
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* uint16 field. This is for historical reasons: before PostgreSQL 7.3,
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* there was no concept of a page version number, and doing it this way
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@ -128,6 +132,7 @@ typedef struct PageHeaderData
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LocationIndex pd_upper; /* offset to end of free space */
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LocationIndex pd_special; /* offset to start of special space */
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uint16 pd_pagesize_version;
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TransactionId pd_prune_xid; /* oldest prunable XID, or zero if none */
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ItemIdData pd_linp[1]; /* beginning of line pointer array */
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} PageHeaderData;
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@ -141,20 +146,14 @@ typedef PageHeaderData *PageHeader;
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* pd_lower. This should be considered a hint rather than the truth, since
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* changes to it are not WAL-logged.
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*
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* PD_PRUNABLE is set if there are any prunable tuples in the page.
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* This should be considered a hint rather than the truth, since
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* the transaction which generates a prunable tuple may or may not commit.
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* Also there is a lag before a tuple is declared dead.
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*
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* PD_PAGE_FULL is set if an UPDATE doesn't find enough free space in the
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* page for its new tuple version; this suggests that a prune is needed.
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* Again, this is just a hint.
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*/
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#define PD_HAS_FREE_LINES 0x0001 /* are there any unused line pointers? */
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#define PD_PRUNABLE 0x0002 /* are there any prunable tuples? */
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#define PD_PAGE_FULL 0x0004 /* not enough free space for new tuple? */
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#define PD_PAGE_FULL 0x0002 /* not enough free space for new tuple? */
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#define PD_VALID_FLAG_BITS 0x0007 /* OR of all valid pd_flags bits */
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#define PD_VALID_FLAG_BITS 0x0003 /* OR of all valid pd_flags bits */
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/*
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* Page layout version number 0 is for pre-7.3 Postgres releases.
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@ -162,7 +161,8 @@ typedef PageHeaderData *PageHeader;
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* Release 8.0 uses 2; it changed the HeapTupleHeader layout again.
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* Release 8.1 uses 3; it redefined HeapTupleHeader infomask bits.
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* Release 8.3 uses 4; it changed the HeapTupleHeader layout again, and
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* added the pd_flags field (by stealing some bits from pd_tli).
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* added the pd_flags field (by stealing some bits from pd_tli),
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* as well as adding the pd_prune_xid field (which enlarges the header).
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*/
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#define PG_PAGE_LAYOUT_VERSION 4
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@ -348,13 +348,6 @@ typedef PageHeaderData *PageHeader;
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#define PageClearHasFreeLinePointers(page) \
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(((PageHeader) (page))->pd_flags &= ~PD_HAS_FREE_LINES)
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#define PageIsPrunable(page) \
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(((PageHeader) (page))->pd_flags & PD_PRUNABLE)
|
||||
#define PageSetPrunable(page) \
|
||||
(((PageHeader) (page))->pd_flags |= PD_PRUNABLE)
|
||||
#define PageClearPrunable(page) \
|
||||
(((PageHeader) (page))->pd_flags &= ~PD_PRUNABLE)
|
||||
|
||||
#define PageIsFull(page) \
|
||||
(((PageHeader) (page))->pd_flags & PD_PAGE_FULL)
|
||||
#define PageSetFull(page) \
|
||||
@ -362,6 +355,22 @@ typedef PageHeaderData *PageHeader;
|
||||
#define PageClearFull(page) \
|
||||
(((PageHeader) (page))->pd_flags &= ~PD_PAGE_FULL)
|
||||
|
||||
#define PageIsPrunable(page, oldestxmin) \
|
||||
( \
|
||||
AssertMacro(TransactionIdIsNormal(oldestxmin)), \
|
||||
TransactionIdIsValid(((PageHeader) (page))->pd_prune_xid) && \
|
||||
TransactionIdPrecedes(((PageHeader) (page))->pd_prune_xid, oldestxmin) \
|
||||
)
|
||||
#define PageSetPrunable(page, xid) \
|
||||
do { \
|
||||
Assert(TransactionIdIsNormal(xid)); \
|
||||
if (!TransactionIdIsValid(((PageHeader) (page))->pd_prune_xid) || \
|
||||
TransactionIdPrecedes(xid, ((PageHeader) (page))->pd_prune_xid)) \
|
||||
((PageHeader) (page))->pd_prune_xid = (xid); \
|
||||
} while (0)
|
||||
#define PageClearPrunable(page) \
|
||||
(((PageHeader) (page))->pd_prune_xid = InvalidTransactionId)
|
||||
|
||||
|
||||
/* ----------------------------------------------------------------
|
||||
* extern declarations
|
||||
|
||||
Loading…
Reference in New Issue
Block a user