From: James Mansion <james@mansionfamily.plus.com>
To: Magnus Hagander <magnus@hagander.net>
Cc: Alexander Staubo <alex@purefiction.net>
Cc: Andy <frum@ar-sd.net>
Cc: pgsql-performance@postgresql.org
Subject: Re: LIKE search and performance
Date: Thu, 24 May 2007 21:54:34 +0100
Message-ID: <4655FB8A.1040707@mansionfamily.plus.com> (raw)
In-Reply-To: <4655E64B.5050503@hagander.net>
References: <009501c79d4c$445428f0$0b00a8c0@mpsro.dom>
<88daf38c0705230905u1a981102k691b47bd36011a80@mail.gmail.com>
<4655DE75.4080506@mansionfamily.plus.com>
<4655E64B.5050503@hagander.net>
> If Sybase is still like SQL Server (or the other way around), it *may*
> end up scanning the index *IFF* the index is a clustered index. If it's
> a normal index, it will do a sequential scan on the table.
>
>
Are you sure its not covered? Have to check at work - but I'm off next
week so it'll have to wait.
> It's not a win on PostgreSQL, because of our MVCC implementation. We
> need to scan *both* index *and* data pages if we go down that route, in
> which case it's a lot faster to just scan the data pages alone.
>
>
Why do you need to go to all the data pages - doesn't the index
structure contain all the keys so
you prefilter and then check to see if the *matched* items are still in
view? I'll be first to admit I
know zip about Postgres, but it seems odd - doesn't the index contain
copies of the key values?.
I suspect that I mis-spoke with 'leaf'. I really just mean 'all index
pages with data', since the scan
does not even need to be in index order, just a good way to get at the
data in a compact way.
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To: pgsql-performance@postgresql.org
Cc: james@mansionfamily.plus.com, magnus@hagander.net, alex@purefiction.net, frum@ar-sd.net
Subject: Re: LIKE search and performance
In-Reply-To: <4655FB8A.1040707@mansionfamily.plus.com>
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