Re: Very long time to execute and Update, suggestions?

Philip Hallstrom wrote:
> I'm not sure about this which is why I'm replying off list, but your
> index is on file_type, file_parent_dir, and file_name and you're query
> is on file_parent_dir and file_name.
>
> I seem to remember reading that that the index will only get used if the
> columns in the where clause "match up" "in order".
>
> That is um... if you have an index on columns a and b and a where clause
> of "b = 1" it woin't use the index since the index "looks like"
>
> a, b
> a, b
> a, b
> etc...
>
> Does that make any sense?  Not sure if that's right or not, but easy
> enough to remove the "file_type" from your index and try it.
>
> post back to the list if that's it.
>
> -philip

Thanks for the reply!

   I have played around a little more and have created a few different
test Indexes and it looks like it is the regex that is causing it to do
the sequential scan. If I remove the regex and create a
'file_parent_dir', 'file_name' index it will use it. If I create an
Index just for 'file_parent_dir' and change my UPDATE to just look for
the regex '... WHERE file_parent_dir~'^/<dir>'...' it will still do the
sequential scan anyway.

   So I need to either find an Index that will work with regexes or
re-write my code to update each subdirectory separately and use simpler
UPDATE statement for each.

   Thanks again!

Madison

PS - I cc'ed the list to follow up on what I found out so far. (Hi list!)


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Madison Kelly (Digimer)
TLE-BU, The Linux Experience; Back Up
http://tle-bu.thelinuxexperience.com
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