just as a by the way, does anybody know of a good mysql mailing group.
I dont have access to news and using Deja is a pain cause we have quite slow
internet access.
thanks,
Justin.
Ryan Mitchell wrote:
> > It only uses table based locking and it treats updates with a higher
> > priority than reads. That means that if you start a read query that takes
> > 60 seconds to execute, you can continue other reads just fine during that
> > period, _until_ you queue an update request on that table. Once you do
> > that, then nothing else (read or write) can access the table until the 60
> > second read finishes, then the update finishes.
> >
> > So even though you are not executing any update that will lock the table
> > and take a long time to do the query, it can still be locked for a long
> > time.
> >
> > It can have quite a significant impact on high traffic websites doing a
> > high number of normally cheap queries, since it backs up the webserver and
> > jserv quite horribly; you have to ensure that your code can gracefully
> > deal with such failures without choking everything up. Otherwise, you can
> > end up in errors being spit back from jserv that look something horrible.
> > This also presents difficulties in running a 24x7 site if you need to do
> > batch updates to info in the database, since you essentially have to take
> > the site offline to do that with mysql.
> >
> > But this is getting off topic...
>
> so to get even further off topic, you can use the DELAYED or
> LOW_PRIORITY inserts and updates features of Mysql to get around these
> table locking issues (LOW_PRIORITY insert or update waits until no other
> clients are reading from the table before running; DELAYED inserts allow
> the client to return immediately while Mysql queues up the inserts for
> later insertion -- see Mysql reference manual for further details) -- so
> in most cases (especially where we don't care about the order in which
> queries get executed) we can have long running queries concurrent with
> quick selects & updates/inserts.
>
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