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Do all Postgres queries touch Shared_Buffers at some point? - Mailing list pgsql-general

From Shiv Sharma
Subject Do all Postgres queries touch Shared_Buffers at some point?
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Msg-id CA+LWa-L+ojx3Myhdq6SfiF-rDGXVOo-dYnE4O6KTnmVSdDo+Jw@mail.gmail.com
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Responses Re: Do all Postgres queries touch Shared_Buffers at some point?  (Michael Paquier <michael.paquier@gmail.com>)
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I am puzzled about the extent to which shared_bufferes is used for different queries.  Do _all_ queries "touch" shared buffers at some point of their execution?

Many of our warehouse queries are  seq_scan followed by HASH.   I know work_mem is assigned for HASH joins:  but does this mean that these queries never touch shared buffers at *all* during their execution?  Perhaps they are read into shared_buffers and then passed into work_mem HASH areas???

What about updates on big tables? What about inserts  on big tables? What about append-inserts? 

I think I could get these answers from Explain Analyze Buffers but I am on 8.2 :-(

Please tell me which queries use/touch shared_buffers in general terms, or please point me to documentation.


Shiv



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