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From: sud <[email protected]>
To: pgsql-general <[email protected]>
Subject: Question on Alerts
Date: Sun, 16 Feb 2025 18:59:38 +0530
Message-ID: <CAD=mzVX2xXh0ruTsyXdjtMPEYv=75tN0Gy+Zcs=PaWiCUvS=RA@mail.gmail.com> (raw)

Hi,
We are asked to have key monitoring or alerting added to our postgres
database. And I am thinking of metrics like blocked transactions, Max used
transaction Ids,  Max Active session threshold, Deadlock, Long running
query,  replica lag, buffer cache hit ratio, read/write IOPS or latency
etc. I have below questions

1)Below are some which i tried writing, can you please let me know if these
are accurate?
2)How should we be writing the alerting query for deadlock, max used
transaction ids, read/write IOPS and latency?
3)Are there any docs available which have these sample sql queries on the
pg_* table for these critical alerts which we can easily configure through
any tool?
4)Any other alerts which we should be really having?

*****Blocking sessions
select distinct blocking_id from
   (
SELECT
    activity.pid,
    activity.usename,
    activity.query,
    blocking.pid AS blocking_id,
    blocking.query AS blocking_query
FROM pg_stat_activity AS activity
JOIN pg_stat_activity AS blocking
    ON blocking.pid = ANY(pg_blocking_pids(activity.pid))
   ) a;

**** long running beyond ~1 hours*****
SELECT
    query,
    datname,
    pid,
    now() - state_change AS idle_for
FROM    pg_stat_activity
WHERE    state IN ('active', 'idle in transaction')
    AND pid <> pg_backend_pid()
    AND xact_start < now() - interval '1 hour'
ORDER BY    age(backend_xmin) DESC NULLS LAST;

**** No of active sessions ******
SELECT count(*) AS active_connections
FROM pg_stat_activity
WHERE state = 'active';

***replica lag****
SELECT client_addr, state, sent_location, write_location, flush_location,
replay_location,
       pg_wal_lsn_diff(sent_location, replay_location) AS replica_lag
FROM pg_stat_replication;

***buffer cache hit ratio****
SELECT
   (1 - (blks_read::float / (blks_hit + blks_read))) * 100 AS
buffer_cache_hit_ratio
FROM pg_stat_database;

Regards
Yudhi

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