Re: PostgreSQL 9.2 - pg_dump out of memory when backuping a database with 300000000 large objects

Try update to the latest release,I see there is a bug fix about pg_dump out
of memroy in 9.2.2,from the release note
http://www.postgresql.org/docs/devel/static/release-9-2-2.html:

-

Work around unportable behavior of malloc(0) and realloc(NULL, 0) (Tom
Lane)

On platforms where these calls return NULL, some code mistakenly thought
that meant out-of-memory. This is known to have broken pg_dump for
databases containing no user-defined aggregates. There might be other cases
as well.

Jov
blog: http:amutu.com/blog <http://amutu.com/blog>

2013/10/1 Sergey Klochkov <klochkov(at)iqbuzz(dot)ru>

> Hello All,
>
> While trying to backup a database of relatively modest size (160 Gb) I ran
> into the following issue:
>
> When I run
> $ pg_dump -f /path/to/mydb.dmp -C -Z 9 mydb
>
> File /path/to/mydb.dmp does not appear (yes, I've checked permissions and
> so on). pg_dump just begins to consume memory until it eats up all
> avaliable RAM (96 Gb total on server, >64 Gb available) and is killed by
> the oom killer.
>
> According to pg_stat_activity, pg_dump runs the following query
>
> SELECT oid, (SELECT rolname FROM pg_catalog.pg_roles WHERE oid = lomowner)
> AS rolname, lomacl FROM pg_largeobject_metadata
>
> until it is killed.
>
> strace shows that pg_dump is constantly reading a large amount of data
> from a UNIX socket. I suspect that it is the result of the above query.
>
> There are >300000000 large objects in the database. Please don't ask me
> why.
>
> I tried googling on this, and found mentions of pg_dump being killed by
> oom killer, but I failed to find anything related to the huge large objects
> number.
>
> Is there any method of working around this issue?
>
> Thanks in advance.
>
> OS: CentOS 6
> PostgreSQL version: 9.2.1
> 96 Gb RAM
>
> PostgreSQL configuration:
>
> listen_addresses = '*' # what IP address(es) to listen on;
> port = 5432 # (change requires restart)
> max_connections = 500 # (change requires restart)
> shared_buffers = 16GB # min 128kB
> temp_buffers = 64MB # min 800kB
> work_mem = 512MB # min 64kB
> maintenance_work_mem = 30000MB # min 1MB
> checkpoint_segments = 70 # in logfile segments, min 1, 16MB
> each
> effective_cache_size = 50000MB
> logging_collector = on # Enable capturing of stderr and
> csvlog
> log_directory = 'pg_log' # directory where log files are
> written,
> log_filename = 'postgresql-%a.log' # log file name pattern,
> log_truncate_on_rotation = on # If on, an existing log file of
> the
> log_rotation_age = 1d # Automatic rotation of logfiles
> will
> log_rotation_size = 0 # Automatic rotation of logfiles
> will
> log_min_duration_statement = 5000
> log_line_prefix = '%t' # special values:
> autovacuum = on # Enable autovacuum subprocess?
> 'on'
> log_autovacuum_min_duration = 0 # -1 disables, 0 logs all actions
> and
> autovacuum_max_workers = 5 # max number of autovacuum
> subprocesses
> autovacuum_naptime = 5s # time between autovacuum runs
> autovacuum_vacuum_threshold = 25 # min number of row updates before
> autovacuum_vacuum_scale_factor = 0.1 # fraction of table size before
> vacuum
> autovacuum_vacuum_cost_delay = 7ms # default vacuum cost delay for
> autovacuum_vacuum_cost_limit = 1500 # default vacuum cost limit for
> datestyle = 'iso, dmy'
> lc_monetary = 'ru_RU.UTF-8' # locale for monetary
> formatting
> lc_numeric = 'ru_RU.UTF-8' # locale for number
> formatting
> lc_time = 'ru_RU.UTF-8' # locale for time
> formatting
> default_text_search_config = 'pg_catalog.russian'
>
> --
> Sergey Klochkov
> klochkov(at)iqbuzz(dot)ru
>
>
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