explanation of some configs - Mailing list pgsql-performance

From Thomas Finneid
Subject explanation of some configs
Date
Msg-id 498CDB41.1010007@fcon.no
Whole thread Raw
Responses Re: explanation of some configs  ("Joshua D. Drake" <jd@commandprompt.com>)
List pgsql-performance
Hi

I am having some problem understanding the details of a couple of
configuration directives. Here  is what I think I understand it so far:

effective_cache_size
    - specifies in how many B/KB/MB will be used to cache data
      between pg and the OS?
    - what is actually cached and how it is actually used by the
           planner and how does it affect the planner and the queries?
      -in other words, when and why do I need to set this parameter?

checkpoint_segments
    - specifies the number of segments?
      size: number*16MB?
    - means when number of WAL segments has filled up and matches
           checkpoint segment, dirty data is written to disk?
    - so it specifies how much data is stored in memory/wal before
           written to disk and therefore affects recoverability?

regards

thomas

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