Susan Hinrichs created TS-4278:
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Summary: HostDB sync causes active transactions to block for 100's
of ms
Key: TS-4278
URL: https://issues.apache.org/jira/browse/TS-4278
Project: Traffic Server
Issue Type: Bug
Components: HostDB
Reporter: Susan Hinrichs
When HostDB syncs to disk (by default every two minutes), active transactions
will block when they reach HttpSM::do_hostdb_lookup. This is because
do_hostdb_lookup calls hostDBProcessor.getbyname_imm which attempts to get the
bucket locks. The delays generally last for 500-1200ms. This blocks the
event loop so no other actions will be performed by the net handler until the
lock is dropped.
I'm assuming that the bucket locks are grabbed by the sync logic. When I
increased proxy.config.cache.hostdb.sync_frequency to 1200, the every two
minute slow down went away. Fortunately
proxy.config.cache.hostdb.sync_frequency set to 0 seems to completely eliminate
the sync, which will be my suggested solution internally.
I tried reducing the size of the hostdb table, but that didn't seem to affect
the delay time.
The delay only reliably exhibited on loaded system. Running my httperf test
case on a machine with no other activity did not show the delays.
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