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Re: Maintaining cluster order on insert

From: "Jim C(dot) Nasby" <decibel(at)decibel(dot)org>
To: Heikki Linnakangas <heikki(at)enterprisedb(dot)com>
Cc: Bruce Momjian <bruce(at)momjian(dot)us>,PostgreSQL-patches <pgsql-patches(at)postgresql(dot)org>
Subject: Re: Maintaining cluster order on insert
Date: 2007-05-16 00:38:10
Message-ID: 20070516003810.GI20707@nasby.net (view raw or flat)
Thread:
Lists: pgsql-hackerspgsql-patches
What about adding the ability to ask the FSM for a page that's near a
given page? That way if you did have to go to the FSM you could at least
try and insert close to the page you originally wanted.

On Tue, May 15, 2007 at 11:26:51PM +0100, Heikki Linnakangas wrote:
> Ah, thanks! I had forgotten about it as well.
> 
> Bruce Momjian wrote:
> >[ Sorry I found this one only found recently.]
> >
> >Your patch has been added to the PostgreSQL unapplied patches list at:
> >
> >	http://momjian.postgresql.org/cgi-bin/pgpatches
> >
> >It will be applied as soon as one of the PostgreSQL committers reviews
> >and approves it.
> >
> >---------------------------------------------------------------------------
> >
> >
> >Heikki Linnakangas wrote:
> >>While thinking about index-organized-tables and similar ideas, it 
> >>occurred to me that there's some low-hanging-fruit: maintaining cluster 
> >>order on inserts by trying to place new heap tuples close to other 
> >>similar tuples. That involves asking the index am where on the heap the 
> >>new tuple should go, and trying to insert it there before using the FSM. 
> >>Using the new fillfactor parameter makes it more likely that there's 
> >>room on the page. We don't worry about the order within the page.
> >>
> >>The API I'm thinking of introduces a new optional index am function, 
> >>amsuggestblock (suggestions for a better name are welcome). It gets the 
> >>same parameters as aminsert, and returns the heap block number that 
> >>would be optimal place to put the new tuple. It's be called from 
> >>ExecInsert before inserting the heap tuple, and the suggestion is passed 
> >>on to heap_insert and RelationGetBufferForTuple.
> >>
> >>I wrote a little patch to implement this for btree, attached.
> >>
> >>This could be optimized by changing the existing aminsert API, because 
> >>as it is, an insert will have to descend the btree twice. Once in 
> >>amsuggestblock and then in aminsert. amsuggestblock could keep the right 
> >>index page pinned so aminsert could locate it quicker. But I wanted to 
> >>keep this simple for now. Another improvement might be to allow 
> >>amsuggestblock to return a list of suggestions, but that makes it more 
> >>expensive to insert if there isn't room in the suggested pages, since 
> >>heap_insert will have to try them all before giving up.
> >>
> >>Comments regarding the general idea or the patch? There should probably 
> >>be a index option to turn the feature on and off. You'll want to turn it 
> >>off when you first load a table, and turn it on after CLUSTER to keep it 
> >>clustered.
> >>
> >>Since there's been discussion on keeping the TODO list more up-to-date, 
> >>I hereby officially claim the "Automatically maintain clustering on a 
> >>table" TODO item :). Feel free to bombard me with requests for status 
> >>reports. And just to be clear, I'm not trying to sneak this into 8.2 
> >>anymore, this is 8.3 stuff.
> >>
> >>I won't be implementing a background daemon described on the TODO item, 
> >>since that would essentially be an online version of CLUSTER. Which sure 
> >>would be nice, but that's a different story.
> >>
> >>- Heikki
> >>
> >
> >
> 
> 
> -- 
>   Heikki Linnakangas
>   EnterpriseDB   http://www.enterprisedb.com
> 
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-- 
Jim Nasby                                      decibel(at)decibel(dot)org
EnterpriseDB      http://enterprisedb.com      512.569.9461 (cell)

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