We have a java-based webapp that talks to MySQL 5.1 INNODB in READ_COMMITTED. We use Hibernate and optimistic concurrency, so periodically concurrent write attempts cause app-level Exceptions that trigger rollbacks (and then we retry tx). We've added app-level caching and turned down our tomcat NIO thread count to just 8 (very little contention inside the app) but now we're seeing that rollbacks appear to be up to 30x slower than commits?! Is that normal?
Here's a typical TX: Set autocommit=0; Select * from users where name="bob"; Update users set visit_count=X where id=bobId and version=Y Commit; Set autocommit=1; When this tx is executed about 100 times/sec, appserver latency is about 10-15 ms per http request (including db time). However, when instead of commit a 'rollback' is issued, the latency spikes to 600-1100 ms (nearly all of that time in appserver appears to be spent waiting on db). So is that expected cost of a rollback? Can anything be done to speed it up? Thanks! -nikita
