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From Mark Matthews <m...@mysql.com>
Subject Re: Tomcat becoming almost completely non-responsive
Date Wed, 06 Oct 2004 01:53:55 GMT
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Kaleb Pederson wrote:
> Hello,
> 
> I have an interesting problem.  After a while, tomcat (5.0.27) becomes almost 
> completely non-responsive.  If I telnet in to port 8009  (I'm using apache 
> and mod_jk2), I get no response, at least not within the default timeout.  If 
> a browse to a page, I will generally, after about 4-5 minutes, see a page 
> returned.
> 
> To narrow down the slowness, I generated a full thread dump, and found the 
> following information:
> 
> [ see attachment for more info]
> Total threads: 180
> executeQuery: 2 //  executing a db query
> validateConnection: 0 // trying to validate their connection
> validateObect: 48 // in commons.dbcp.PoolableConnectionFactory.validateObject
> socketAccept: 3 // accepting a socket
> socketRead0: 10 // reading a socket
> ReferenceQueue: 1
> ThreadPool$MonitorRunnable: 2
> borrowObject and Object.wait: 85 // trying to get an object from the pool
> Object.wait: 20 // threads just waiting around
> Remaining:  9 // misc. threads
> 
> My database connection is setup so that I have 50 allowed connections, which 
> matches my 48 in validateObject and 2 executing queries.  However, when I 
> query the database status, I see 2 active threads and the rest are 
> 'sleeping', just waiting around, as they would be if the connection pool 
> hadn't released them yet.
> 
> So, why would there be 48 connections that seemed locked and weren't querying 
> the DB?  And then the other 85 that were seemingly waiting on the 45?  Any 
> ideas what might be going on?  The DB is ready?  I have log abandoned turned 
> and an haven't seen a problem yet.  If the load drops sufficiently on the 
> server, everything eventually returns back to normal, otherwise it takes 5-10 
> minutes to get a response from the server.
> 
> I have attached an abbreviated form of the thread dump which should provide 
> all the critical information and can provide as much other information as is 
> necessary.
> 
> Thanks for the help.  *All* suggestions welcome ;)
> 
> --Kaleb
> 
> 
> ------------------------------------------------------------------------
> 
> Total threads: 180
> executeQuery: 2
> validateConnection: 0
> validateObect: 48
> socketAccept: 3
> socketRead0: 10
> ReferenceQueue: 1
> ThreadPool$MonitorRunnable: 2
> borrowObject and Object.wait: 85
> borrowObject: 0
> Object.wait: 20
> Remaining:  9
> ***************************************************
> 2 like "TP-Processor296" daemon prio=1 tid=0x6ea04a90 nid=0x5e87 runnable [738f6000..738f787c]
> 	at java.net.SocketInputStream.socketRead0(Native Method)
> 	at java.net.SocketInputStream.read(SocketInputStream.java:129)
> 	at java.io.BufferedInputStream.fill(BufferedInputStream.java:183)
> 	at java.io.BufferedInputStream.read1(BufferedInputStream.java:222)
> 	at java.io.BufferedInputStream.read(BufferedInputStream.java:277)
[snip]

Kaleb,

Looks like you're using an old version of the JDBC driver that uses
BufferedInputStreams by default. There is a 'feature' (many call a bug)
in BufferedInputStreams that causes them in some cases to want to read a
full buffer's worth of data when you're only asking for some portion of
it...That's what's happening here.

I'd try downloading something more recent for a JDBC driver (like
Connector/J 3.0.15) and see where that gets you, to start with.

	-Mark

- --
Mr. Mark Matthews
MySQL AB, Software Development Manager, J2EE and Windows Platforms
Office: +1 708 332 0507
www.mysql.com

MySQL Guide to Lower TCO
http://www.mysql.com/it-resources/white-papers/tco.php
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