Bug #32877 loadBalanceStrategy=bestResponseTime hangs forever on a single unreachable host
Submitted: 30 Nov 2007 16:40 Modified: 25 Feb 13:14
Reporter: Domas Mituzas
Status: Closed
Category:Connector/J Severity:S3 (Non-critical)
Version:5.1-20071127 OS:Any
Assigned to: Target Version:

[30 Nov 2007 16:40] Domas Mituzas 
Description:
If loadBalanceStrategy=bestResponseTime is used and an unreachable host is attempted to
connect to, conn/j will repeatedly try to connect to it (probably because response time is
not initialized...). 

How to repeat:
Connection string:

jdbc:mysql:loadbalance://192.168.1.5:3306,localhost:3306/test?failOverReadOnly=false&loadB
alanceStrategy=bestResponseTime&autoReconnectForPools=true&connectTimeout=100

.1.5 is down in this case. 

if bestResponseTime is not used, connectTimeout works properly, otherwise JVM attempts
reconnects to same host every 100ms or so. 

Suggested fix:
do not retry same host in case of bestResponseTime strategy, especially if it fails.
[30 Nov 2007 20:30] Bugs System 
A patch for this bug has been committed. After review, it may
be pushed to the relevant source trees for release in the next
version. You can access the patch from:

  http://lists.mysql.com/commits/39010
[4 Dec 2007 17:16] Bugs System 
A patch for this bug has been committed. After review, it may
be pushed to the relevant source trees for release in the next
version. You can access the patch from:

  http://lists.mysql.com/commits/39227
[25 Feb 13:14] MC Brown 
A note has been added to the 5.1.6 changelog: 

Load balancing connection using best response time would incorrectly "stick" to hosts that
were down when the connection was first created.

We solve this problem with a black list that is used during the picking of new hosts. If
the black list ends up including all configured hosts, the driver will retry for a
configurable number of times (the retriesAllDown configuration property, with a default of
120 times), sleeping 250ms between attempts to pick a new connection.

We've also went ahead and made the balancing strategy extensible. To create a new
strategy, implement the interface com.mysql.jdbc.BalanceStrategy (which also includes our
standard "extension" interface), and tell the driver to use it by passing in the class
name via the loadBalanceStrategy configuration property.