If the subtransaction cache is overflowed in some of the transactions
then it will affect all the concurrent queries as they need to access
the SLRU for checking the visibility of each tuple. But currently
there is no way to identify whether in any backend subtransaction is
overflowed or what is the current active subtransaction count.
Attached patch adds subtransaction count and subtransaction overflow
status in pg_stat_activity. I have implemented this because of the
recent complain about the same[1]
[1] https://www.postgresql.org/message-id/CAFiTN-t5BkwdHm1bV8ez64guWZJB_Jjhb7arsQsftxEwpYwObg%40mail.gmail.com
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Regards,
Dilip Kumar
EnterpriseDB: http://www.enterprisedb.com