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Re: Hash Indexes

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On Tue, Jan 08, 2008 at 01:49:53AM +1100, Naz Gassiep wrote:
> Because doing normal queries on a table where there are large text 
> blocks is unlikely to be a good idea. E.g.,:
> 
> SELECT * FROM table WHERE textcol = 'a 4kb block of text';

I suggest you look at the tsearch stuff instead.

> I would assume that hash indexes have inbuilt mechanisms for collision 
> checking before returning the row as a match. Am I correct in this 
> assumption?

I think you should avoid any assumptions about the hash index implementation
in PostgreSQL.  The general consensus seems to be that the code has a number
of problems.  Most importantly, hash index operations are _not_ currently
WAL-logged, which means you probably need to REINDEX in the event of a
database crash.  I don't know whether the collision issues are present in
hash indexes, though.

A


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