With about 400 records total - as I said in my original post - , I should imagine that any elapsed time will be more a function of my connection speed than a true measure of database/query speed.
At 11:56 22/12/02 -0400, Adolfo Bello wrote:
Create 2 tables with identical columns definition, one with index and the other without.Start adding records to the two tables and querying them. This way you'll find out the number of recors for which the performance is about the same. After that, you can decide wich way to go. Adolfo > -----Original Message----- > From: Mark Matthews [mailto:[EMAIL PROTECTED]] > Sent: Sunday, December 22, 2002 9:44 AM > To: Iain Lang > Cc: Alan McDonald; [EMAIL PROTECTED] > Subject: Re: How long is my piece of string? > > > -----BEGIN PGP SIGNED MESSAGE----- > Hash: SHA1 > > Iain Lang wrote: > > . > > But that is my question! *When* do they provide a > performance difference? > > Obviously my (fairly simple) question ("...and beyond what number of > > records might indices provide faster > extraction/presentation?... ) has > > not been understood. Can anyone else help, please? > > > > At 11:22 22/12/02 +1100, Alan McDonald wrote: > > > >> You need indexes as soon as (or rather just before) they provide a > >> performance difference. > > From http://www.mysql.com/doc/en/Where_optimisations.html : > > "Each table index is queried, and the best index that spans > fewer than > 30% of the rows is used. If no such index can be found, a quick table > scan is used.". > > So if you can't create an index that will have values that will cause > MySQL to look at less that 30% of the rows, it will not be used. For > example if you have a column that contains the value 'foo' 90% of the > time, queries looking for 'foo' in that column will not use an index. > > Indexes almost _always_ slow down data _modification_. You can tell > when/if they speed-up data retrieval by using the 'EXPLAIN' > command in > MySQL, see: > http://www.mysql.com/doc/en/EXPLAIN.html -Mark -----BEGIN PGP SIGNATURE----- Version: GnuPG v1.1.90 (MingW32) Comment: Using GnuPG with Mozilla - http://enigmail.mozdev.org iD8DBQE+BcGPtvXNTca6JD8RAjAmAKC/OlCFFx7iLZN57AMIRO5cV4wfyACgrLjU OHViqL0GR0Hf4lLoS50uTXU= =veUT -----END PGP SIGNATURE----- --------------------------------------------------------------------- Before posting, please check: http://www.mysql.com/manual.php (the manual) http://lists.mysql.com/ (the list archive) To request this thread, e-mail <[EMAIL PROTECTED]> To unsubscribe, e-mail <[EMAIL PROTECTED]> Trouble unsubscribing? Try: http://lists.mysql.com/php/unsubscribe.php
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