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Commit2b5819e

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Do not summarize WAL if generated with wal_level=minimal.
To do this, we must include the wal_level in the first WAL recordcovered by each summary file; so add wal_level to struct Checkpointand the payload of XLOG_CHECKPOINT_REDO and XLOG_END_OF_RECOVERY.This, in turn, requires bumping XLOG_PAGE_MAGIC and, since theCheckpoint is also stored in the control file, alsoPG_CONTROL_VERSION. It's not great to do that so late in the releasecycle, but the alternative seems to ship v17 without robustprotections against this scenario, which could result in corruptedincremental backups.A side effect of this patch is that, when a server withwal_level=replica is started with summarize_wal=on for the first time,summarization will no longer begin with the oldest WAL that stillexists in pg_wal, but rather from the first checkpoint after that.This change should be harmless, because a WAL summary for a partialcheckpoint cycle can never make an incremental backup possible whenit would otherwise not have been.Report by Fujii Masao. Patch by me. Review and/or testing by JakubWartak and Fujii Masao.Discussion:http://postgr.es/m/6e30082e-041b-4e31-9633-95a66de76f5d@oss.nttdata.com
1 parent4cbd8c6 commit2b5819e

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9 files changed

+278
-81
lines changed

9 files changed

+278
-81
lines changed

‎doc/src/sgml/config.sgml

Lines changed: 11 additions & 5 deletions
Original file line numberDiff line numberDiff line change
@@ -4318,11 +4318,17 @@ restore_command = 'copy "C:\\server\\archivedir\\%f" "%p"' # Windows
43184318
<listitem>
43194319
<para>
43204320
Enables the WAL summarizer process. Note that WAL summarization can
4321-
be enabled either on a primary or on a standby. WAL summarization
4322-
cannot be enabled when <varname>wal_level</varname> is set to
4323-
<literal>minimal</literal>. This parameter can only be set in the
4324-
<filename>postgresql.conf</filename> file or on the server command line.
4325-
The default is <literal>off</literal>.
4321+
be enabled either on a primary or on a standby. This parameter can only
4322+
be set in the <filename>postgresql.conf</filename> file or on the server
4323+
command line. The default is <literal>off</literal>.
4324+
</para>
4325+
<para>
4326+
The server cannot be started with <literal>summarize_wal=on</literal>
4327+
if <literal>wal_level</literal> is set to <literal>minimal</literal>. If
4328+
<literal>summarize_wal=on</literal> is configured after server startup
4329+
while <literal>wal_level=minimal</literal>, the summarizer will run
4330+
but refuse to generate summary files for any WAL generated with
4331+
<literal>wal_level=minimal</literal>.
43264332
</para>
43274333
</listitem>
43284334
</varlistentry>

‎doc/src/sgml/func.sgml

Lines changed: 11 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -27960,6 +27960,17 @@ SELECT currval(pg_get_serial_sequence('sometable', 'id'));
2796027960
not running, it will be equal to <literal>summarized_lsn</literal>.
2796127961
<literal>summarizer_pid</literal> is the PID of the WAL summarizer
2796227962
process, if it is running, and otherwise NULL.
27963+
</para>
27964+
<para>
27965+
As a special exception, the WAL summarizer will refuse to generate
27966+
WAL summary files if run on WAL generated under
27967+
<literal>wal_level=minimal</literal>, since such summaries would be
27968+
unsafe to use as the basis for an incremental backup. In this case,
27969+
the fields above will continue to advance as if summaries were being
27970+
generated, but nothing will be written to disk. Once the summarizer
27971+
reaches WAL generated while <literal>wal_level</literal> was set
27972+
to <literal>replica</literal> or higher, it will resume writing
27973+
summaries to disk.
2796327974
</para></entry>
2796427975
</row>
2796527976
</tbody>

‎src/backend/access/rmgrdesc/xlogdesc.c

Lines changed: 31 additions & 16 deletions
Original file line numberDiff line numberDiff line change
@@ -33,6 +33,27 @@ const struct config_enum_entry wal_level_options[] = {
3333
{NULL,0, false}
3434
};
3535

36+
/*
37+
* Find a string representation for wal_level
38+
*/
39+
staticconstchar*
40+
get_wal_level_string(intwal_level)
41+
{
42+
conststructconfig_enum_entry*entry;
43+
constchar*wal_level_str="?";
44+
45+
for (entry=wal_level_options;entry->name;entry++)
46+
{
47+
if (entry->val==wal_level)
48+
{
49+
wal_level_str=entry->name;
50+
break;
51+
}
52+
}
53+
54+
returnwal_level_str;
55+
}
56+
3657
void
3758
xlog_desc(StringInfobuf,XLogReaderState*record)
3859
{
@@ -45,14 +66,15 @@ xlog_desc(StringInfo buf, XLogReaderState *record)
4566
CheckPoint*checkpoint= (CheckPoint*)rec;
4667

4768
appendStringInfo(buf,"redo %X/%X; "
48-
"tli %u; prev tli %u; fpw %s; xid %u:%u; oid %u; multi %u; offset %u; "
69+
"tli %u; prev tli %u; fpw %s;wal_level %s;xid %u:%u; oid %u; multi %u; offset %u; "
4970
"oldest xid %u in DB %u; oldest multi %u in DB %u; "
5071
"oldest/newest commit timestamp xid: %u/%u; "
5172
"oldest running xid %u; %s",
5273
LSN_FORMAT_ARGS(checkpoint->redo),
5374
checkpoint->ThisTimeLineID,
5475
checkpoint->PrevTimeLineID,
5576
checkpoint->fullPageWrites ?"true" :"false",
77+
get_wal_level_string(checkpoint->wal_level),
5678
EpochFromFullTransactionId(checkpoint->nextXid),
5779
XidFromFullTransactionId(checkpoint->nextXid),
5880
checkpoint->nextOid,
@@ -95,20 +117,9 @@ xlog_desc(StringInfo buf, XLogReaderState *record)
95117
{
96118
xl_parameter_changexlrec;
97119
constchar*wal_level_str;
98-
conststructconfig_enum_entry*entry;
99120

100121
memcpy(&xlrec,rec,sizeof(xl_parameter_change));
101-
102-
/* Find a string representation for wal_level */
103-
wal_level_str="?";
104-
for (entry=wal_level_options;entry->name;entry++)
105-
{
106-
if (entry->val==xlrec.wal_level)
107-
{
108-
wal_level_str=entry->name;
109-
break;
110-
}
111-
}
122+
wal_level_str=get_wal_level_string(xlrec.wal_level);
112123

113124
appendStringInfo(buf,"max_connections=%d max_worker_processes=%d "
114125
"max_wal_senders=%d max_prepared_xacts=%d "
@@ -135,9 +146,10 @@ xlog_desc(StringInfo buf, XLogReaderState *record)
135146
xl_end_of_recoveryxlrec;
136147

137148
memcpy(&xlrec,rec,sizeof(xl_end_of_recovery));
138-
appendStringInfo(buf,"tli %u; prev tli %u; time %s",
149+
appendStringInfo(buf,"tli %u; prev tli %u; time %s; wal_level %s",
139150
xlrec.ThisTimeLineID,xlrec.PrevTimeLineID,
140-
timestamptz_to_str(xlrec.end_time));
151+
timestamptz_to_str(xlrec.end_time),
152+
get_wal_level_string(xlrec.wal_level));
141153
}
142154
elseif (info==XLOG_OVERWRITE_CONTRECORD)
143155
{
@@ -150,7 +162,10 @@ xlog_desc(StringInfo buf, XLogReaderState *record)
150162
}
151163
elseif (info==XLOG_CHECKPOINT_REDO)
152164
{
153-
/* No details to write out */
165+
intwal_level;
166+
167+
memcpy(&wal_level,rec,sizeof(int));
168+
appendStringInfo(buf,"wal_level %s",get_wal_level_string(wal_level));
154169
}
155170
}
156171

‎src/backend/access/transam/xlog.c

Lines changed: 4 additions & 4 deletions
Original file line numberDiff line numberDiff line change
@@ -6934,6 +6934,7 @@ CreateCheckPoint(int flags)
69346934
WALInsertLockAcquireExclusive();
69356935

69366936
checkPoint.fullPageWrites=Insert->fullPageWrites;
6937+
checkPoint.wal_level=wal_level;
69376938

69386939
if (shutdown)
69396940
{
@@ -6987,11 +6988,9 @@ CreateCheckPoint(int flags)
69876988
*/
69886989
if (!shutdown)
69896990
{
6990-
intdummy=0;
6991-
6992-
/* Record must have payload to avoid assertion failure. */
6991+
/* Include WAL level in record for WAL summarizer's benefit. */
69936992
XLogBeginInsert();
6994-
XLogRegisterData((char*)&dummy,sizeof(dummy));
6993+
XLogRegisterData((char*)&wal_level,sizeof(wal_level));
69956994
(void)XLogInsert(RM_XLOG_ID,XLOG_CHECKPOINT_REDO);
69966995

69976996
/*
@@ -7314,6 +7313,7 @@ CreateEndOfRecoveryRecord(void)
73147313
elog(ERROR,"can only be used to end recovery");
73157314

73167315
xlrec.end_time=GetCurrentTimestamp();
7316+
xlrec.wal_level=wal_level;
73177317

73187318
WALInsertLockAcquireExclusive();
73197319
xlrec.ThisTimeLineID=XLogCtl->InsertTimeLineID;

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