Re: Swap on postgres master server - Mailing list pgsql-general

I guess you can run swapoff (followed by swapon).  That will free up
whatever is currently swapped.  Beware if the system is actively
swapping then swapoff can take some time.  But it seems not in your
case.
On Tue, 16 Oct 2018 at 10:48, Nicola Contu <nicola.contu@gmail.com> wrote:
>
> No it is not probably used, because I can't find it in any way as I said.
>
> I run your commands :
>
> [root@usnyh-cmd1 ~]# vmstat 1
> procs -----------memory---------- ---swap-- -----io---- -system-- ------cpu-----
>  r  b   swpd   free   buff  cache   si   so    bi    bo   in   cs us sy id wa st
>  3  2 7505332 14545468  13692 241436784    0    0    47   115    0    0 11  2 84  2  0
>  3  2 7505332 14490408  13692 241436928    0    0     0   248 6153 2013  3  1 93  3  0
>  1  2 7505332 14474672  13692 241436800    0    0     0  1124 4905 1454  3  1 93  3  0
>  4  2 7505332 14381156  13692 241436832    0    0     0    96 5322 1782  2  1 94  3  0
> ^C
> [root@usnyh-cmd1 ~]# ps -A --sort -rss -o comm,pmem | awk '
> >   NR == 1 { print; next }
> >   { a[$1] += $2 }
> >   END {
> >     for (i in a) {
> >       printf "%-15s\t%s\n", i, a[i];
> >     }
> >   }
> > '
> COMMAND         %MEM
> kworker/42:2    0
> kworker/60:6H  0
> kworker/60:2H  0
> kdmwork-253:2  0
> ksoftirqd/60    0
> postmaster      15.2
> kworker/9:0H    0
>
> So I'm just asking why it is still there with free -m and if there is any way to free that up if it is not used.
>
> Thanks
>
> Il giorno mar 16 ott 2018 alle ore 11:18 Hans Schou <hans.schou@gmail.com> ha scritto:
>>
>> Are you sure that swap is used actively? Maybe it had just been used during backup or something.
>>
>> Look after SwapIn/SwapOut (si/so) it should be '0'
>> $ vmstat 1
>> procs -----------memory---------- ---swap-- -----io---- -system-- ------cpu-----
>>  r  b   swpd   free   buff  cache   si   so    bi    bo   in   cs us sy id wa st
>>  1  0     12  89344  46608 586384    0    0    12     8   30   86  0  0 99  0  0
>>
>> If you want to see the amount of ram used by each program with childs run this:
>> ps -A --sort -rss -o comm,pmem | awk '
>>   NR == 1 { print; next }
>>   { a[$1] += $2 }
>>   END {
>>     for (i in a) {
>>       printf "%-15s\t%s\n", i, a[i];
>>     }
>>   }
>> '
>>
>>
>> On Tue, Oct 16, 2018 at 11:04 AM Nicola Contu <nicola.contu@gmail.com> wrote:
>>>
>>> Hello,
>>> we are running Postgres 10.5 with master slave replication.
>>>
>>> These are our custom params
>>>
>>> archive_command = 'pgbackrest --stanza=cmdprod archive-push %p' # command to use to archive a logfile segment
>>> archive_mode = on # enables archiving; off, on, or always
>>> checkpoint_completion_target = 0.7 # checkpoint target duration, 0.0 - 1.0
>>> default_text_search_config = 'pg_catalog.english' #
>>> datestyle = 'iso, mdy' #
>>> effective_cache_size = 120GB #
>>> hot_standby = on                        # "on" allows queries during recovery
>>> lc_messages = 'en_US.UTF-8'                      # locale for system error message
>>> lc_monetary = 'en_US.UTF-8'                      # locale for monetary formatting
>>> lc_numeric = 'en_US.UTF-8'                      # locale for number formatting
>>> lc_time = 'en_US.UTF-8'                          # locale for time formatting
>>> listen_addresses = '*' # defaults to 'localhost', '*' = all
>>> log_autovacuum_min_duration = 1000ms        # -1 disables, 0 logs all actions and
>>> log_checkpoints = on #
>>> log_line_prefix = '%t [%r] [%p]: [%l-1] db=%d,user=%u ' #
>>> log_lock_waits = on                      # log lock waits >= deadlock_timeout
>>> log_min_duration_statement = 1000ms        # -1 is disabled, 0 logs all statements
>>> log_statement = 'ddl'                  # none, ddl, mod, all
>>> log_temp_files = 1024kB                      # log temporary files equal or larger
>>> maintenance_work_mem = 2GB #
>>> max_connections = 220 #
>>> max_parallel_workers_per_gather = 8        # taken from max_worker_processes
>>> max_wal_size = 2GB #
>>> min_wal_size = 1GB #
>>> pg_stat_statements.max = 10000 #
>>> pg_stat_statements.track = all #
>>> port = 5432                            # port number which Postgres listen
>>> shared_buffers = 10GB #
>>> shared_preload_libraries = 'pg_stat_statements'          # (change requires restart)
>>> synchronous_standby_names = '1 ( "usnyh2" )' # comment out during upgrade
>>> track_activity_query_size = 16384        # (change requires restart)
>>> track_io_timing = on #
>>> wal_buffers = 16MB #
>>> wal_keep_segments = 100 #
>>> wal_level = replica                    #  minimal, replica, or logical
>>> work_mem = 600MB #
>>>
>>> This server is on Centos 7 and the strange thing is that we see a lot of swap usage :
>>>
>>> [root@usnyh-cmd1 ~]# free -m
>>>               total        used        free      shared  buff/cache   available
>>> Mem:         257652        7555        5559       12804      244536      236036
>>> Swap:         16383        7326        9057
>>>
>>> 7GB used.
>>>
>>> But can't see it from any of the commands like top etc.
>>> I am sure it is postgres because it is the only service running on that machine.
>>>
>>> Is there anything we can do?
>>> On the sync slave, the usage is just 400MB.
>>>
>>> Any trick?
>>>
>>> Thanks a lot,
>>> Nicola