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https://issues.apache.org/jira/browse/ZOOKEEPER-1767?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Patrick Hunt updated ZOOKEEPER-1767:
------------------------------------
Assignee: Jackie Chang
> DEBUG log statements use SLF4j {} format to improve performance
> ---------------------------------------------------------------
>
> Key: ZOOKEEPER-1767
> URL: https://issues.apache.org/jira/browse/ZOOKEEPER-1767
> Project: ZooKeeper
> Issue Type: Improvement
> Affects Versions: 3.4.5
> Reporter: Jackie Chang
> Assignee: Jackie Chang
> Priority: Minor
> Attachments: ZOOKEEPER-1767-correct-indents.patch,
> ZOOKEEPER-1767-slf4j.patch
>
>
> As a coordination service, ZooKeeper is meant to be high performant. DEBUG
> logs are not normally viewed (see Doug Cutting's comment in HADOOP-953). I
> propose to add a conditional check to each DEBUG log stmt to improve
> performance.
> Firstly, previous issues added a condition check before a DEBUG log stmt. For
> example, in ZOOKEEPER-558:
> {code}
> - LOG.debug("Got notification sessionid:0x"
> - + Long.toHexString(sessionId));
> + if (LOG.isDebugEnabled()) {
> + LOG.debug("Got notification sessionid:0x" +
> + Long.toHexString(sessionId));
> + }
> {code}
> And in ZOOKEEPER-259:
> {code}
> - LOG
> - .debug("Got ping sessionid:0x"
> - + Long.toHexString(sessionId));
> + if (LOG.isDebugEnabled()) {
> + LOG.debug("Got ping response for sessionid:0x"
> + + Long.toHexString(sessionId)
> + + " after "
> + + ((System.nanoTime() - lastPingSentNs) /
> 1000000)
> + + "ms");
> + }
> {code}
> Secondly, its underlying cause is that:
> * *If a DEBUG log stmt is unguarded, the string operations (most likely
> concatenations) are actually conducted even though the log event doesn't
> happen b/c a level less verbose than DEBUG is configured.*
> * Adding the conditional check creates another basic block in Java bytecode.
> And instructions inside that basicblock is executed only when execution path
> goes into it. But this only happens when the path passes the test. Detailed
> explanations are in a StackOverflow thread:
> http://stackoverflow.com/questions/10428447/log-debug-enabled-check-in-java
> An alternative solution is to move from log4j to slf4j and use the "{}"
> format. A workaround now is to add all conditional checks. The additional
> overhead is marginal (possibly compare-and-jump instruction(s) in Java
> bytecode) compared to saved computation of expensive string creations and
> concatenations.
> Its counterpart in Hadoop has been accepted: HADOOP-6884.
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