[ZOOKEEPER-974] Configurable listen socket backlog for the client port

• Type: Improvement
• Status: Resolved
• Priority: Minor
• Resolution: Fixed
• Affects Version/s: 3.3.2
• Fix Version/s: 3.6.0
• Component/s: server
• Labels: pull-request-available
• Tags: backlog
• Assignee: Josh Elser
• Reporter: Hoonmin Kim
• Created: 10/Jan/11 08:35
• Updated: 04/Oct/19 14:55
• Resolved: 13/Feb/19 12:13

Description

We're running ZooKeeper ensemble(3-node configuration) for production use for months.
Days ago, we suffered temporary network? problems that caused many reconnections(about 300) of ephemeral nodes in one ZooKeeper server.

The almost all clients successfully reconnected to the other ZooKeeper servers,
but one client failed to reconnect in time and got a session expired message from the server.
(The problem is that our clients died when they got SessionExpired message.)

There were many listenQ overflows/drops and out resets in a minute just before the problem situation.

—

So we patched ZooKeeper to increase the backlog size for the client port socket to avoid unhappy cases like this.
As ZooKeeper uses default backlog size(50) to bind(), we added "clientPortBacklog" option.

Though the default backlog should be good for common environment,
we believe that configuring the size is also meaningful.

[Note]
On linux, below parameter :

net.core.somaxconn

needs to be larger than above "clientPortBacklog" to correctly configure listen socket backlog

Issue Links

• links to: GitHub Pull Request #784