Re: MultiXact member wraparound protections are disabled

[avi Singh <avisingh19811981@xxxxxxxxx>]

Got the output of pg_control

postgres@site-db01a:~/cmates/data/global $ /usr/pgsql-9.4/bin/pg_controldata  /var/lib/pgsql/cmates/data
pg_control version number:            942
Catalog version number:               201409291
Database system identifier:           6228991221455883206
Database cluster state:               in production
pg_control last modified:             Wed 12 Oct 2016 07:08:14 PM PDT
Latest checkpoint location:           62E1/890DA8D8
Prior checkpoint location:            62E0/550B2178
Latest checkpoint's REDO location:    62E1/4F054A08
Latest checkpoint's REDO WAL file:    00000001000062E10000004F
Latest checkpoint's TimeLineID:       1
Latest checkpoint's PrevTimeLineID:   1
Latest checkpoint's full_page_writes: on
Latest checkpoint's NextXID:          1/1834454859
Latest checkpoint's NextOID:          19540816
Latest checkpoint's NextMultiXactId:  784527
Latest checkpoint's NextMultiOffset:  1445313
Latest checkpoint's oldestXID:        226141373
Latest checkpoint's oldestXID's DB:   16457
Latest checkpoint's oldestActiveXID:  1834454859
Latest checkpoint's oldestMultiXid:   1
Latest checkpoint's oldestMulti's DB: 16457
Time of latest checkpoint:            Wed 12 Oct 2016 07:06:45 PM PDT
Fake LSN counter for unlogged rels:   0/1
Minimum recovery ending location:     0/0
Min recovery ending loc's timeline:   0
Backup start location:                0/0
Backup end location:                  0/0
End-of-backup record required:        no
Current wal_level setting:            hot_standby
Current wal_log_hints setting:        off
Current max_connections setting:      1500
Current max_worker_processes setting: 8
Current max_prepared_xacts setting:   0
Current max_locks_per_xact setting:   1000
Maximum data alignment:               8
Database block size:                  8192
Blocks per segment of large relation: 131072
WAL block size:                       8192
Bytes per WAL segment:                16777216
Maximum length of identifiers:        64
Maximum columns in an index:          32
Maximum size of a TOAST chunk:        1996
Size of a large-object chunk:         2048
Date/time type storage:               64-bit integers
Float4 argument passing:              by value
Float8 argument passing:              by value
Data page checksum version:           0

On Wed, Oct 12, 2016 at 7:10 PM, avi Singh <avisingh19811981@xxxxxxxxx> wrote:

Sharing output

postgres@site-db01a:~/cmates/data/pg_multixact/members $ ls
0000  0002  0004  0006  0008  000A  000C  000E  0010  0012  0014  0016  0018  001A
0001  0003  0005  0007  0009  000B  000D  000F  0011  0013  0015  0017  0019  001B

postgres@site-db01a:~/cmates/data/pg_multixact/offsets $ ls
0001  0002  0003  0004  0005  0006  0007  0008  0009  000A  000B


postgres@site-db01a:/tmp $ /usr/pgsql-9.4/bin/pg_controldata -D /var/lib/pgsql/cmates/data
pg_controldata: could not open file "-D/global/pg_control" for reading: No such file or directory

pg_controldata is not working in here even though the file is there inside global but it is not reading from it

postgres@site-db01a:~/cmates/data/global $ ls -la pg_control
-rw-------. 1 postgres postgres 8192 Oct 12 18:55 pg_control

On Wed, Oct 12, 2016 at 4:58 PM, Alvaro Herrera <alvherre@xxxxxxxxxxxxxxx> wrote:

AnandKumar, Karthik wrote:
> Hi,
>
> We run postgres 9.4.5.
>
> Starting this morning, we started seeing messages like the below:
> Oct 12 14:07:15 site-db01a postgres[11253]: [106430-1] app=,user=,db=,ip=LOG:  MultiXact member wraparound protections are disabled because oldest checkpointed MultiXact 1 does not exist on disk
> Oct 12 14:09:26 site-db01a postgres[11253]: [106526-1] app=,user=,db=,ip=LOG:  MultiXact member wraparound protections are disabled because oldest checkpointed MultiXact 1 does not exist on disk
> Oct 12 14:14:18 site-db01a postgres[11253]: [106608-1] app=,user=,db=,ip=LOG:  MultiXact member wraparound protections are disabled because oldest checkpointed MultiXact 1 does not exist on disk
>
> Our autovacuum_freeze_max_age = 1750000000.
>
> site=# SELECT datname, age(datfrozenxid) FROM pg_database;
>  datname  |    age
> -----------+------------
> site      | 1645328344
> template0 | 1274558807
> bench     | 1274558807
> postgres  | 1324283514
> template1 | 1274558807
>
> So we’re about 100 mil transactions away before we start vacuuming to prevent wraparound.
>
> We’re running precautionary vacuums on our largest offenders to try and drop our transaction ids
>
> What I’d request some clarity on is the message above. What does it mean that "oldest checkpointed MultiXact does not exist on disk”? Would we lose data if we did have to wrap around?
>
> Is this telling us we’re not vacuuming effectively enough?

Ugh.  Can you share the output of pg_controldata and the list of files
in pg_multixact/members and pg_multixact/offset?

The problem here is that multixact vacuuming is separate from xid
vacuuming, so you need to be looking at datminmulti rather than
datfrozenxid.  It may be that multixact wrap around has already
occurred.

--
Álvaro Herrera                https://www.2ndQuadrant.com/
PostgreSQL Development, 24x7 Support, Remote DBA, Training & Services


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