| From: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
|---|---|
| To: | "Aaron Werman" <awerman2(at)hotmail(dot)com> |
| Cc: | "Iain" <iain(at)mst(dot)co(dot)jp>, "Jim C(dot) Nasby" <decibel(at)decibel(dot)org>, pgsql-performance(at)postgresql(dot)org |
| Subject: | Re: Caching of Queries |
| Date: | 2004-09-28 13:58:01 |
| Message-ID: | 14083.1096379881@sss.pgh.pa.us |
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| Lists: | pgsql-performance |
"Aaron Werman" <awerman2(at)hotmail(dot)com> writes:
> I imagine a design where a shared plan cache would consist of the plans,
> indexed by a statement hash and again by dependant objects. A statement to
> be planned would be hashed and matched to the cache. DDL would need to
> synchronously destroy all dependant plans. If each plan maintains a validity
^^^^^^^^^^^^^
> flag, changing the cache wouldn't have to block so I don't see where there
^^^^^^^^^^^^^^^^^^^^^^
> would be contention.
You have contention to access a shared data structure *at all* -- for
instance readers must lock out writers. Or didn't you notice the self-
contradictions in what you just said?
Our current scalability problems dictate reducing such contention, not
adding whole new sources of it.
regards, tom lane
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