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Commitbc7d37a

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Transaction IDs wrap around, per my proposal of 13-Aug-01. More
documentation to come, but the code is all here. initdb forced.
1 parentd1ee78f commitbc7d37a

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29 files changed

+615
-169
lines changed

29 files changed

+615
-169
lines changed

‎doc/src/sgml/catalogs.sgml‎

Lines changed: 25 additions & 2 deletions
Original file line numberDiff line numberDiff line change
@@ -1,6 +1,6 @@
11
<!--
22
Documentation of the system catalogs, directed toward PostgreSQL developers
3-
$Header: /cvsroot/pgsql/doc/src/sgml/catalogs.sgml,v 2.21 2001/08/21 16:35:58 tgl Exp $
3+
$Header: /cvsroot/pgsql/doc/src/sgml/catalogs.sgml,v 2.22 2001/08/26 16:55:58 tgl Exp $
44
-->
55

66
<chapter id="catalogs">
@@ -840,11 +840,34 @@
840840
<entry><type>oid</type></entry>
841841
<entry></entry>
842842
<entry>
843-
Lastoidinexistence afterthe database was created; useful
843+
Lastsystem OIDin the database; useful
844844
particularly to <application>pg_dump</application>
845845
</entry>
846846
</row>
847847

848+
<row>
849+
<entry>datvacuumxid</entry>
850+
<entry><type>xid</type></entry>
851+
<entry></entry>
852+
<entry>
853+
All tuples inserted or deleted by transaction IDs before this one
854+
have been marked as known committed or known aborted in this database.
855+
This is used to determine when commit-log space can be recycled.
856+
</entry>
857+
</row>
858+
859+
<row>
860+
<entry>datfrozenxid</entry>
861+
<entry><type>xid</type></entry>
862+
<entry></entry>
863+
<entry>
864+
All tuples inserted by transaction IDs before this one have been
865+
relabeled with a permanent (<quote>frozen</>) transaction ID in this
866+
database. This is useful to check whether a database must be vacuumed
867+
soon to avoid transaction ID wraparound problems.
868+
</entry>
869+
</row>
870+
848871
<row>
849872
<entry>datpath</entry>
850873
<entry><type>text</type></entry>

‎doc/src/sgml/ref/create_database.sgml‎

Lines changed: 15 additions & 1 deletion
Original file line numberDiff line numberDiff line change
@@ -1,5 +1,5 @@
11
<!--
2-
$Header: /cvsroot/pgsql/doc/src/sgml/ref/create_database.sgml,v 1.17 2000/11/15 19:43:39 petere Exp $
2+
$Header: /cvsroot/pgsql/doc/src/sgml/ref/create_database.sgml,v 1.18 2001/08/26 16:55:59 tgl Exp $
33
Postgres documentation
44
-->
55

@@ -284,6 +284,20 @@ comment from Olly; response from Thomas...
284284
simply by setting the flag false). The <literal>template0</literal>
285285
database is normally marked this way to prevent modification of it.
286286
</para>
287+
288+
<para>
289+
After preparing a template database, or making any changes to one,
290+
it is a good idea to perform
291+
<command>VACUUM FREEZE</> or <command>VACUUM FULL FREEZE</> in that
292+
database. If this is done when there are no other open transactions
293+
in the same database, then it is guaranteed that all tuples in the
294+
database are <quote>frozen</> and will not be subject to transaction
295+
ID wraparound problems. This is particularly important for a database
296+
that will have <literal>datallowconn</literal> set to false, since it
297+
will be impossible to do routine maintenance <command>VACUUM</>s on
298+
such a database.
299+
See the Administrator's Guide for more information.
300+
</para>
287301
</refsect2>
288302
</refsect1>
289303

‎doc/src/sgml/ref/vacuum.sgml‎

Lines changed: 37 additions & 12 deletions
Original file line numberDiff line numberDiff line change
@@ -1,5 +1,5 @@
11
<!--
2-
$Header: /cvsroot/pgsql/doc/src/sgml/ref/vacuum.sgml,v 1.17 2001/07/10 22:09:28 tgl Exp $
2+
$Header: /cvsroot/pgsql/doc/src/sgml/ref/vacuum.sgml,v 1.18 2001/08/26 16:55:59 tgl Exp $
33
Postgres documentation
44
-->
55

@@ -20,11 +20,11 @@ Postgres documentation
2020
</refnamediv>
2121
<refsynopsisdiv>
2222
<refsynopsisdivinfo>
23-
<date>2001-07-10</date>
23+
<date>2001-08-26</date>
2424
</refsynopsisdivinfo>
2525
<synopsis>
26-
VACUUM [ FULL ] [ VERBOSE ] [ <replaceable class="PARAMETER">table</replaceable> ]
27-
VACUUM [ FULL ] [ VERBOSE ] ANALYZE [ <replaceable class="PARAMETER">table</replaceable> [ (<replaceable class="PARAMETER">column</replaceable> [, ...] ) ] ]
26+
VACUUM [ FULL ] [FREEZE ] [VERBOSE ] [ <replaceable class="PARAMETER">table</replaceable> ]
27+
VACUUM [ FULL ] [FREEZE ] [VERBOSE ] ANALYZE [ <replaceable class="PARAMETER">table</replaceable> [ (<replaceable class="PARAMETER">column</replaceable> [, ...] ) ] ]
2828
</synopsis>
2929

3030
<refsect2 id="R2-SQL-VACUUM-1">
@@ -46,6 +46,14 @@ VACUUM [ FULL ] [ VERBOSE ] ANALYZE [ <replaceable class="PARAMETER">table</repl
4646
</para>
4747
</listitem>
4848
</varlistentry>
49+
<varlistentry>
50+
<term>FREEZE</term>
51+
<listitem>
52+
<para>
53+
Selects aggressive <quote>freezing</quote> of tuples.
54+
</para>
55+
</listitem>
56+
</varlistentry>
4957
<varlistentry>
5058
<term>VERBOSE</term>
5159
<listitem>
@@ -169,21 +177,38 @@ NOTICE: Index <replaceable class="PARAMETER">index</replaceable>: Pages 28;
169177
</para>
170178

171179
<para>
172-
Plain <command>VACUUM</command> simply reclaims space and makes it
180+
<command>VACUUM ANALYZE</command> performs a <command>VACUUM</command>
181+
and then an <command>ANALYZE</command> for each selected table. This
182+
is a handy combination form for routine maintenance scripts. See
183+
<xref linkend="sql-analyze" endterm="sql-analyze-title">
184+
for more details about its processing.
185+
</para>
186+
187+
<para>
188+
Plain <command>VACUUM</command> (without <literal>FULL</>) simply reclaims
189+
space and makes it
173190
available for re-use. This form of the command can operate in parallel
174191
with normal reading and writing of the table. <command>VACUUM
175192
FULL</command> does more extensive processing, including moving of tuples
176193
across blocks to try to compact the table to the minimum number of disk
177-
blocks. This is much slower and requires an exclusive lock on each table
178-
while it is being processed.
194+
blocks. Thisformis much slower and requires an exclusive lock on each
195+
tablewhile it is being processed.
179196
</para>
180197

181198
<para>
182-
<command>VACUUM ANALYZE</command> performs a <command>VACUUM</command>
183-
and then an <command>ANALYZE</command> for each selected table. This
184-
is a handy combination form for routine maintenance scripts. See
185-
<xref linkend="sql-analyze" endterm="sql-analyze-title">
186-
for more details about its processing.
199+
<command>FREEZE</command> is a special-purpose option that
200+
causes tuples to be marked <quote>frozen</quote> as soon as possible,
201+
rather than waiting until they are quite old. If this is done when there
202+
are no other open transactions in the same database, then it is guaranteed
203+
that all tuples in the database are <quote>frozen</> and will not be
204+
subject to transaction ID wraparound problems, no matter how long the
205+
database is left un-vacuumed.
206+
<command>FREEZE</command> is not recommended for routine use. Its only
207+
intended usage is in connection with preparation of user-defined template
208+
databases, or other databases that are completely read-only and will not
209+
receive routine maintenance <command>VACUUM</> operations.
210+
See <xref linkend="sql-createdatabase" endterm="sql-createdatabase-title">
211+
for details.
187212
</para>
188213

189214
<refsect2 id="R2-SQL-VACUUM-3">

‎src/backend/access/transam/clog.c‎

Lines changed: 19 additions & 3 deletions
Original file line numberDiff line numberDiff line change
@@ -13,7 +13,7 @@
1313
* Portions Copyright (c) 1996-2001, PostgreSQL Global Development Group
1414
* Portions Copyright (c) 1994, Regents of the University of California
1515
*
16-
* $Header: /cvsroot/pgsql/src/backend/access/transam/clog.c,v 1.2 2001/08/25 23:24:39 tgl Exp $
16+
* $Header: /cvsroot/pgsql/src/backend/access/transam/clog.c,v 1.3 2001/08/26 16:55:59 tgl Exp $
1717
*
1818
*-------------------------------------------------------------------------
1919
*/
@@ -762,8 +762,12 @@ ExtendCLOG(TransactionId newestXact)
762762
{
763763
intpageno;
764764

765-
/* No work except at first XID of a page */
766-
if (TransactionIdToPgIndex(newestXact)!=0)
765+
/*
766+
* No work except at first XID of a page. But beware: just after
767+
* wraparound, the first XID of page zero is FirstNormalTransactionId.
768+
*/
769+
if (TransactionIdToPgIndex(newestXact)!=0&&
770+
!TransactionIdEquals(newestXact,FirstNormalTransactionId))
767771
return;
768772

769773
pageno=TransactionIdToPage(newestXact);
@@ -818,6 +822,18 @@ TruncateCLOG(TransactionId oldestXact)
818822
S_LOCK(&(ClogCtl->control_lck));
819823

820824
restart:;
825+
/*
826+
* While we are holding the lock, make an important safety check:
827+
* the planned cutoff point must be <= the current CLOG endpoint page.
828+
* Otherwise we have already wrapped around, and proceeding with the
829+
* truncation would risk removing the current CLOG segment.
830+
*/
831+
if (CLOGPagePrecedes(ClogCtl->latest_page_number,cutoffPage))
832+
{
833+
S_UNLOCK(&(ClogCtl->control_lck));
834+
elog(LOG,"unable to truncate commit log: apparent wraparound");
835+
return;
836+
}
821837

822838
for (slotno=0;slotno<NUM_CLOG_BUFFERS;slotno++)
823839
{

‎src/backend/access/transam/transam.c‎

Lines changed: 66 additions & 1 deletion
Original file line numberDiff line numberDiff line change
@@ -8,7 +8,7 @@
88
*
99
*
1010
* IDENTIFICATION
11-
* $Header: /cvsroot/pgsql/src/backend/access/transam/transam.c,v 1.47 2001/08/25 18:52:41 tgl Exp $
11+
* $Header: /cvsroot/pgsql/src/backend/access/transam/transam.c,v 1.48 2001/08/26 16:55:59 tgl Exp $
1212
*
1313
* NOTES
1414
* This file contains the high level access-method interface to the
@@ -236,3 +236,68 @@ TransactionIdAbort(TransactionId transactionId)
236236

237237
TransactionLogUpdate(transactionId,TRANSACTION_STATUS_ABORTED);
238238
}
239+
240+
241+
/*
242+
* TransactionIdPrecedes --- is id1 logically < id2?
243+
*/
244+
bool
245+
TransactionIdPrecedes(TransactionIdid1,TransactionIdid2)
246+
{
247+
/*
248+
* If either ID is a permanent XID then we can just do unsigned
249+
* comparison. If both are normal, do a modulo-2^31 comparison.
250+
*/
251+
int32diff;
252+
253+
if (!TransactionIdIsNormal(id1)|| !TransactionIdIsNormal(id2))
254+
return (id1<id2);
255+
256+
diff= (int32) (id1-id2);
257+
return (diff<0);
258+
}
259+
260+
/*
261+
* TransactionIdPrecedesOrEquals --- is id1 logically <= id2?
262+
*/
263+
bool
264+
TransactionIdPrecedesOrEquals(TransactionIdid1,TransactionIdid2)
265+
{
266+
int32diff;
267+
268+
if (!TransactionIdIsNormal(id1)|| !TransactionIdIsNormal(id2))
269+
return (id1 <=id2);
270+
271+
diff= (int32) (id1-id2);
272+
return (diff <=0);
273+
}
274+
275+
/*
276+
* TransactionIdFollows --- is id1 logically > id2?
277+
*/
278+
bool
279+
TransactionIdFollows(TransactionIdid1,TransactionIdid2)
280+
{
281+
int32diff;
282+
283+
if (!TransactionIdIsNormal(id1)|| !TransactionIdIsNormal(id2))
284+
return (id1>id2);
285+
286+
diff= (int32) (id1-id2);
287+
return (diff>0);
288+
}
289+
290+
/*
291+
* TransactionIdFollowsOrEquals --- is id1 logically >= id2?
292+
*/
293+
bool
294+
TransactionIdFollowsOrEquals(TransactionIdid1,TransactionIdid2)
295+
{
296+
int32diff;
297+
298+
if (!TransactionIdIsNormal(id1)|| !TransactionIdIsNormal(id2))
299+
return (id1 >=id2);
300+
301+
diff= (int32) (id1-id2);
302+
return (diff >=0);
303+
}

‎src/backend/access/transam/xid.c‎

Lines changed: 26 additions & 21 deletions
Original file line numberDiff line numberDiff line change
@@ -6,55 +6,44 @@
66
* Portions Copyright (c) 1996-2001, PostgreSQL Global Development Group
77
* Portions Copyright (c) 1994, Regents of the University of California
88
*
9-
*$Id: xid.c,v 1.32 2001/08/23 23:06:37 tgl Exp $
10-
*
11-
* OLD COMMENTS
12-
* XXX WARNING
13-
*Much of this file will change when we change our representation
14-
*of transaction ids -cim 3/23/90
15-
*
16-
* It is time to make the switch from 5 byte to 4 byte transaction ids
17-
* This file was totally reworked. -mer 5/22/92
9+
*$Id: xid.c,v 1.33 2001/08/26 16:55:59 tgl Exp $
1810
*
1911
*-------------------------------------------------------------------------
2012
*/
2113

2214
#include"postgres.h"
2315

16+
#include<limits.h>
17+
2418
#include"access/xact.h"
2519

20+
2621
#definePG_GETARG_TRANSACTIONID(n)DatumGetTransactionId(PG_GETARG_DATUM(n))
2722
#definePG_RETURN_TRANSACTIONID(x)return TransactionIdGetDatum(x)
2823

2924

3025
Datum
3126
xidin(PG_FUNCTION_ARGS)
3227
{
33-
char*representation=PG_GETARG_CSTRING(0);
28+
char*str=PG_GETARG_CSTRING(0);
3429

35-
PG_RETURN_TRANSACTIONID((TransactionId)atol(representation));
30+
PG_RETURN_TRANSACTIONID((TransactionId)strtoul(str,NULL,0));
3631
}
3732

3833
Datum
3934
xidout(PG_FUNCTION_ARGS)
4035
{
4136
TransactionIdtransactionId=PG_GETARG_TRANSACTIONID(0);
4237
/* maximum 32 bit unsigned integer representation takes 10 chars */
43-
char*representation=palloc(11);
38+
char*str=palloc(11);
4439

45-
snprintf(representation,11,"%lu", (unsigned long)transactionId);
40+
snprintf(str,11,"%lu", (unsigned long)transactionId);
4641

47-
PG_RETURN_CSTRING(representation);
42+
PG_RETURN_CSTRING(str);
4843
}
4944

50-
/* ----------------------------------------------------------------
51-
*xideq
52-
* ----------------------------------------------------------------
53-
*/
54-
5545
/*
56-
*xideq- returns 1, iff xid1 == xid2
57-
* 0 else;
46+
*xideq- are two xids equal?
5847
*/
5948
Datum
6049
xideq(PG_FUNCTION_ARGS)
@@ -64,3 +53,19 @@ xideq(PG_FUNCTION_ARGS)
6453

6554
PG_RETURN_BOOL(TransactionIdEquals(xid1,xid2));
6655
}
56+
57+
/*
58+
*xid_age- compute age of an XID (relative to current xact)
59+
*/
60+
Datum
61+
xid_age(PG_FUNCTION_ARGS)
62+
{
63+
TransactionIdxid=PG_GETARG_TRANSACTIONID(0);
64+
TransactionIdnow=GetCurrentTransactionId();
65+
66+
/* Permanent XIDs are always infinitely old */
67+
if (!TransactionIdIsNormal(xid))
68+
PG_RETURN_INT32(INT_MAX);
69+
70+
PG_RETURN_INT32((int32) (now-xid));
71+
}

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