Hi Mark, On Mon, Nov 9, 2015 at 5:42 AM, Mark Triggs <m...@dishevelled.net> wrote:
> While running a benchmark where multiple workers PUT records via > Marmotta's LDP interface, I noticed that all but one of the threads were > waiting on a lock inside the JVM. The code in question was this > `synchronized` block in KiWiValueFactory.createStatement: > > > https://github.com/dpla/marmotta/blob/master/libraries/kiwi/kiwi-triplestore/src/main/java/org/apache/marmotta/kiwi/sail/KiWiValueFactory.java#L567 > > This code takes a lock on the `registry` object (shared by all > connections), and holds it while calling connection.getTripleId(). That > query is generally pretty fast, but it's called frequently enough that the > cost of the locking can still be quite high. > I'm aware of that lock... we need it for ensuring the id generation consistency, but we also know there is room for improvement. > I ran a test where 5 concurrent writers each PUT random records via > Marmotta's LDP interface. I ran 6 test rounds, with each round adding an > extra millisecond delay to the getTripleId() call (simulating between 0 and > 5 milliseconds of network/database latency). As that query gets slower, the > effect of the Java locking becomes more dramatic, as you can see from the > response times here: > > http://dishevelled.net/marmotta-coarse-locking-all-responses.png > > With no added delay (and Postgres running on the same machine as > Marmotta), most PUT requests complete within about 500ms. With 5 > milliseconds of delay, the same PUT requests take between 2.5 and 3 seconds. > > I reworked the code to reduce the time that lock was held, and reran my > test. You can see the response times are much better, even with 5ms of > latency: > > http://dishevelled.net/marmotta-fine-locking-all-responses.png > Indeed it behaves now much better :-) I've got a patch for this that I'm happy to send along. I drop the lock > prior to running the getTripleId() query (allowing multiple connections to > run the query at once), then only take it again if I need to write a new > triple ID to the registry: > > > https://github.com/marktriggs/marmotta/blob/mst-perf/libraries/kiwi/kiwi-triplestore/src/main/java/org/apache/marmotta/kiwi/sail/KiWiValueFactory.java#L578 > Cool! In principle the refactoring in the lock strategy sounds good for me. Then please: first register an issue in our jira, and then create a PR with out patch using the issue key in the name. We'll discuss the patch in dev@marmotta, so please join that mailing list for Thanks, Mark! -- Sergio Fernández Partner Technology Manager Redlink GmbH m: +43 6602747925 e: sergio.fernan...@redlink.co w: http://redlink.co
