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many sessions waiting DataFileRead and extend - Mailing list pgsql-performance

From James Pang
Subject many sessions waiting DataFileRead and extend
Date
Msg-id CAHgTRfdDkiX5bLRCYhrP18kFJjcvs1eHvL+jUtX1Ep-Y3=cFVg@mail.gmail.com
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Responses Re: many sessions waiting DataFileRead and extend
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   pgv14, RHEL8, xfs , we suddenly see tens of sessions waiting on "DataFileRead" and "extend", it last about 2 seconds(based on pg_stat_activity query) , during the waiting time, "%sys" cpu increased to 80% , but from "iostat" , no high iops and io read/write latency increased either.  
   many sessions were running same "DELETE FROM xxxx" in parallel waiting on "extend" and "DataFileRead", there are triggers in this table "After delete" to insert/delete other tables in the tigger. 

time                                                 wait_event                count(sessions)
 2025-06-24 18:00:11.687245+00 | DataFileFlush           |     1
 2025-06-24 18:00:11.687245+00 | DataFileWrite            |     1
 2025-06-24 18:00:11.687245+00 | PgSleep                    |     1
 2025-06-24 18:00:11.687245+00 | DataFileExtend          |     7
 2025-06-24 18:00:11.687245+00 | ProcArrayGroupUpdate |     1
 2025-06-24 18:00:11.687245+00 | WALWrite                    |     5
 2025-06-24 18:00:11.687245+00 | extend                         |    55
 2025-06-24 18:00:11.687245+00 | DataFileRead              |    45
 2025-06-24 18:00:11.687245+00 | DataFilePrefetch         |     2
 
Thanks,

James 

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