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https://issues.apache.org/jira/browse/TS-4278?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Thomas Jackson resolved TS-4278.
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Resolution: Fixed
I merged the new hostdb caching layer in today-- so this issue is no more!
> 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
> Assignee: Thomas Jackson
> Fix For: 7.0.0
>
>
> 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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