On Fri, 5 Oct 2001, Dan Nelson wrote: > This rules out mysql as the cause for the delay.
I agree. > > > I'd say start dumping packets on the network. > > > > I'd agree, but I'm confused as to why a different query (that > > requests more data; 33 rows vs 1) can reliably execute and fetch in > > 10ms on all machines? The behaviour is completely reproducible: > > SELECT (1 record) ON PRIMARY KEY = slow (200ms), SELECT (lots of > > records on indexed field) = fast (10ms) > > The fact that your two queries take different times to process has > nothing to do with indices, and more to do with the bytecount of the > query and the response. > > > > 200ms sounds a lot like Nagle's Algorithm kicking in (which > > > shouldn't happen assuming the mysql libs are written right). > > > > Indeed, I wouldn't have thought they'd have included that! Isn't > > Nagle restricted to telnet? But anyway, not all queries perform > > equally badly. > > Nagle's algorithm applies to all TCP sessions unless explicitly > disabled. It buffers outgoing data less than your MSS for up to 200ms > if there is unacknowleged data already on the wire. This is usually > triggered by inefficient code on the sending end that does multiple > writes(); the first write() gets sent immediately. Any subsequent > writes() get buffered up by Nagle until 200ms or the ACK for the first > block of data from the receiving machine. The standard fix is to > rewrite the sending code to send all its data in a single write(), but > the simple fix (which ends up wasting bandwidth by sending many small > packets) is to > > int var=1; > setsockopt(socket, IPPROTO_TCP, TCP_NODELAY, &var, sizeof(var)); > > Chances are your two windows machines have differnt myodbc versions, or > different TCP settings in the registry, that make Nagle kick in at > different times. Great. That is exactly what I was trying to point out in my last post. But done really poorly. tt, -- Boyd Gerber <[EMAIL PROTECTED]> ZENEZ 3748 Valley Forge Road, Magna Utah 84044 Office 801-250-0795 FAX 801-250-7975 --------------------------------------------------------------------- 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
