Solr Lock Contention

Michael Sun shows how the Apache Solr team found and fixed a performance issue in their code:

Based on this testing, lock contention, which usually results in a performance bottleneck and underutilized resources, was our first “suspect.” We knew that using a commercial Java profiler, such as Yourkit, JProfiler and Java Flight Recorder, would help easily identify locks and determine how much time threads spend waiting on them. Meanwhile, the team had built custom infrastructure that allows one to run experiments with a profiler attached via a single command-line parameter.

In my own testing, the profiler data indeed revealed some contention particularly related to VersionBucket andHdfsUpdateLog locks, leading to long thread wait time. Although promisingly, this result corresponded somewhat to the description in SOLR-6820, nothing actionable resulted from the experiment.

I like these sorts of case studies because example is the school of mankind.  In this particular case, I really like the methodical approach, using available information to search for a root cause.  Some of the things Michael calls “false starts” I would consider to be initial steps:  checking OS, filesystem, and garbage collection metrics are important even in a case like this in which they did not lead to the culprit, as they help you eliminate suspects.

Related Posts

Lock Promotion

Erik Darling tries to figure out why his locks can’t get ahead in the rat race: The first thing I found is that there were 16 attempts at promotion, and four successful promotions.Why did this seem weird? I dunno.Why would there be only 4 successful attempts with no competing locks from other queries?Why wouldn’t all […]

Read More

Thoughts On Exclusive Locks

Louis Davidson shares some thoughts on exclusive locks in SQL Server: You will find that the SELECT statement executes, ignoring the exclusive lock, because it is not a write lock, and the data on the page has not been changed.The main reason people try to do this is to force access to a row in […]

Read More

Categories

August 2016
MTWTFSS
« Jul Sep »
1234567
891011121314
15161718192021
22232425262728
293031