Chad Sollis wrote:
pretty big change performance-wise for the better or worse? what is a
potential negative outcome of dirty reads?
Thanks for all this info.
~Chad
On 8/7/07, Ben Reece <[EMAIL PROTECTED]> wrote:
The other engines have options to allow dirty reads, but MyISAM
doesn't, unless use the MySQL handlers instead of queries, but it's a
lot more work.
The InnoDB engine allows dirty reads, but it can be a pretty big change
performance-wise, depending on how you're using it.
Though in the specified example, if a delete like that is taking a long
time, either a) the row data is very large, b) there are an insane
number of rows, or c) the server's pretty slow. Even deleting 1/2 of a
million rows, it should only take a few seconds, and can be run once a
day during non-peak times.
Ben
Generally MyISAM is more efficient than InnoDB, since it doesn't support
any of the fancy features that InnoDB does. So in this case switching
to InnoDB would probably hurt performance.
Dirty reads are when you pull data from a table while it's being
changed. For example, if I do a 'SELECT * FROM foo' while a 'DELETE
FROM foo WHERE bar < foobar' is running, I might get some of the records
that match the 'DELETE' statement, but not all of them. In the case of
a session DB, dirty reads shouldn't matter at all, since I imagine
you're only pulling 1 row at a time.
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