Zookeeper drops connections under moderate IO load
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Key: ZOOKEEPER-885
URL: https://issues.apache.org/jira/browse/ZOOKEEPER-885
Project: Zookeeper
Issue Type: Bug
Components: server
Affects Versions: 3.2.2
Environment: Debian (Lenny)
1Gb RAM
swap disabled
100Mb heap for zookeeper
Reporter: Alexandre Hardy
Priority: Critical
A zookeeper server under minimum load, with a number of clients watching
exactly one node will fail to maintain the connection when the machine is
subjected to moderate IO load.
In a specific test example we had three zookeeper servers running on dedicated
machines with 45 clients connected, watching exactly one node. The clients
would disconnect after moderate load was added to each of the zookeeper servers
with the command:
{noformat}
dd if=/dev/urandom of=/dev/mapper/nimbula-test
{noformat}
The {{dd}} command transferred data at a rate of about 4Mb/s.
The same thing happens with
{noformat}
dd if=/dev/zero of=/dev/mapper/nimbula-test
{noformat}
transferring at a rate of about 20Mb/s.
It seems strange that such a moderate load should cause instability in the
connection.
Very few other processes were running, the machines were setup to test the
connection instability we have experienced. Clients performed no other read or
mutation operations.
Although the documents state that minimal competing IO load should present on
the zookeeper server, it seems reasonable that moderate IO should not cause
problems in this case.
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