Re: Swap on postgres master server

[Nicola Contu <nicola.contu@xxxxxxxxx>]

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@xxxxxxxxx> 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@xxxxxxxxx> 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