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Data Bases > Pgsql Performance > Re: Exact index...
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Re: Exact index overhead

by dev@[EMAIL PROTECTED] (Richard Huxton) Apr 17, 2008 at 11:00 AM

Gunther Mayer wrote:
> You see, all updates change most of the data fields but never ever touch

> the time field. Assuming correct and efficient behaviour of postgresql 
> it should then also never touch the time index and incur zero overhead 
> in its presence, but is this really the case? If it somehow does update 
> the index too even though the value hasn't changed by some weird 
> implementation detail I'd rather not have that index and live with slow 
> queries for the few times a day that re****ting is run.

Well, until 8.3 PG does indeed update the index. That's because with 
MVCC an update is basically a delete+insert, so you'll end up with two 
versions (the V in MVCC) of the row.

With 8.3 there's a new feature called HOT which means updates that don't 
change an index can be more efficient.

So - if you are running 8.3, I'd say try the index and see what 
difference it makes.

-- 
   Richard Huxton
   Archonet Ltd

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 6 Posts in Topic:
Exact index overhead
gunther.mayer@[EMAIL PROT  2008-04-17 11:27:35 
Re: Exact index overhead
dev@[EMAIL PROTECTED] (R  2008-04-17 11:00:14 
Re: Exact index overhead
heikki@[EMAIL PROTECTED]   2008-04-17 13:02:47 
Re: Exact index overhead
pavan.deolasee@[EMAIL PRO  2008-04-17 15:46:05 
Re: Exact index overhead
gunther.mayer@[EMAIL PROT  2008-04-17 17:42:05 
Re: Exact index overhead
scott.marlowe@[EMAIL PROT  2008-04-19 10:48:42 

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