William,
On 9/7/23 08:04, William Crowell wrote:
When I set -Djdk.tracePinnedThreads=short, then I see this:
…
Thread[#41,ForkJoinPool-1-worker-4,5,CarrierThreads]
com.mysql.cj.jdbc.ConnectionImpl.isValid(ConnectionImpl.java:2516) <==
monitors:1
Thread[#39,ForkJoinPool-1-worker-2,5,CarrierThreads]
com.mysql.cj.jdbc.ConnectionImpl.isValid(ConnectionImpl.java:2516) <==
monitors:1
Thread[#41,ForkJoinPool-1-worker-4,5,CarrierThreads]
com.mysql.cj.jdbc.ConnectionImpl.setAutoCommit(ConnectionImpl.java:2005)
<== monitors:1
Thread[#43,ForkJoinPool-1-worker-5,5,CarrierThreads]
com.mysql.cj.jdbc.ClientPreparedStatement.executeInternal(ClientPreparedStatement.java:893)
<== monitors:1
com.mysql.cj.jdbc.ClientPreparedStatement.executeUpdateInternal(ClientPreparedStatement.java:1061)
<== monitors:1
com.mysql.cj.jdbc.ClientPreparedStatement.executeUpdateInternal(ClientPreparedStatement.java:1009)
<== monitors:1
Thread[#43,ForkJoinPool-1-worker-5,5,CarrierThreads]
com.mysql.cj.jdbc.ConnectionImpl.commit(ConnectionImpl.java:791) <==
monitors:1
Thread[#43,ForkJoinPool-1-worker-5,5,CarrierThreads]
com.mysql.cj.jdbc.ConnectionImpl.setAutoCommit(ConnectionImpl.java:2005)
<== monitors:1
…
I started digging into the MySQL client code:
https://github.com/mysql/mysql-connector-j/blob/8.0.33/src/main/user-impl/java/com/mysql/cj/jdbc/ConnectionImpl.java
This class is littered with synchronized blocks, so now this makes sense to me
why virtual threads would take longer than a regular OS thread.
This is precisely the kind of thing I was expecting to see.
If your "application code" (which includes everything your application
does, including calling into libraries) contains lots of "synchronized"
blocks, then I think this is the situation you will often find yourself in.
I would expect that if you were to increase the size of the virtual
thread pool things would start to get better, but in order to truly use
virtual threads effectively, you have to track-down and eliminate many
uses of synchronized blocks and methods in both your application and the
libraries you use.
I wouldn't expect virtual threads to become a very widely-deployed
performance-optimization technique in the immediate future. I expect
that, eventually, lots of code will be re-written to be more
virtual-thread-friendly.
-chris
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