Re: Streaming replica hangs periodically for ~ 1 second - how to diagnose/debug - Mailing list pgsql-general

On Wed, Aug 20, 2025 at 06:30:00PM +0100, Thom Brown wrote:
> Do you have THP enabled? Can you use mpstat and see what %steal shows as?

Sorry, what is "THP"? I tried searching for "what is thp", and most
common search results are related to some chemical compound.

mpstat, yes, we have it. Let me quickly show what I get:

Two days ago, at ~ 10:10pm UTC I saw this in Pg logs:

# grep -oP '^2025-08-19 22:09:2\d\.\d+ UTC' postgresql-2025-08-19_220000.csv | uniq -c | grep -C3 -P '^\s*\d\d'
      2 2025-08-19 22:09:29.084 UTC
      1 2025-08-19 22:09:29.094 UTC
      2 2025-08-19 22:09:29.097 UTC
     70 2025-08-19 22:09:29.109 UTC
     90 2025-08-19 22:09:29.110 UTC
      6 2025-08-19 22:09:29.111 UTC
      1 2025-08-19 22:09:29.153 UTC
      1 2025-08-19 22:09:29.555 UTC

As you can see we have 70, and then 90 messages all logged with the same
timestamp. All of them (160) were "duration:x" lines.

At the time, mpstat (called using `mpstat 5`) looked like this:

             CPU    %usr   %nice    %sys %iowait    %irq   %soft  %steal  %guest  %gnice   %idle
22:09:04     all    2.25    0.00    0.27    0.24    0.00    0.10    0.00    0.00    0.00   97.14
22:09:09     all    2.70    0.00    0.28    0.27    0.00    0.12    0.00    0.00    0.00   96.63
22:09:14     all    2.83    0.00    0.63    0.23    0.00    0.09    0.00    0.00    0.00   96.22
22:09:19     all    2.66    0.00    0.28    0.23    0.00    0.10    0.00    0.00    0.00   96.74
22:09:24     all    2.36    0.00    0.27    0.21    0.00    0.10    0.00    0.00    0.00   97.06
22:09:29     all    2.49    0.00    0.40    0.40    0.00    0.11    0.00    0.00    0.00   96.60
22:09:34     all    2.65    0.00    0.28    0.23    0.00    0.11    0.00    0.00    0.00   96.73
22:09:39     all    2.26    0.00    0.26    0.21    0.00    0.09    0.00    0.00    0.00   97.19
22:09:44     all    2.31    0.00    0.25    0.22    0.00    0.09    0.00    0.00    0.00   97.13
22:09:49     all    2.44    0.00    0.22    0.24    0.00    0.08    0.00    0.00    0.00   97.02
22:09:54     all    2.23    0.00    0.23    0.28    0.00    0.10    0.00    0.00    0.00   97.16
22:09:59     all    2.48    0.00    0.26    0.30    0.00    0.11    0.00    0.00    0.00   96.85
22:10:04     all    2.29    0.00    0.28    0.26    0.00    0.12    0.00    0.00    0.00   97.06
22:10:09     all    2.31    0.00    0.22    0.21    0.00    0.11    0.00    0.00    0.00   97.14
22:10:14     all    2.38    0.00    0.25    0.21    0.00    0.10    0.00    0.00    0.00   97.05
22:10:19     all    2.54    0.00    0.24    0.20    0.00    0.11    0.00    0.00    0.00   96.91
22:10:24     all    2.26    0.00    0.25    0.22    0.00    0.10    0.00    0.00    0.00   97.17
22:10:29     all    2.12    0.00    0.27    0.24    0.00    0.09    0.00    0.00    0.00   97.27
22:10:34     all    2.56    0.00    0.26    0.26    0.00    0.12    0.00    0.00    0.00   96.80
22:10:39     all    2.16    0.00    0.23    0.24    0.00    0.10    0.00    0.00    0.00   97.27
22:10:44     all    2.37    0.00    0.26    0.22    0.00    0.10    0.00    0.00    0.00   97.05
22:10:49     all    2.25    0.00    0.25    0.61    0.00    0.09    0.00    0.00    0.00   96.80
22:10:54     all    2.41    0.00    0.28    0.22    0.00    0.10    0.00    0.00    0.00   96.99
22:10:59     all    2.83    0.00    0.29    0.19    0.00    0.12    0.00    0.00    0.00   96.57

Best regards,

depesz