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The log server lock is pretty visible in perf top when using log samples because it's taken for each server in turn while trying to validate and update the log server's index. Let's change this for a CAS, since we have the index and the range at hand now. This allow us to remove the logsrv lock. The test on 4 servers now shows a 3.7 times improvement thanks to much lower contention. Without log sampling a test producing 4.4M logs/s delivers 4.4M logs/s at 21 CPUs used, everything spent in the kernel. After enabling 4 samples (1:4, 2:4, 3:4 and 4:4), the throughput would previously drop to 1.13M log/s with 37 CPUs used and 75% spent in process_send_log(). Now with this change, 4.25M logs/s are emitted, using 26 CPUs and 22% in process_send_log(). That's a 3.7x throughput improvement for a 30% global CPU usage reduction, but in practice it mostly shows that the performance drop caused by having samples is much less noticeable (each of the 4 servers has its index updated for each log). Note that in order to even avoid incrementing an index for each log srv that is consulted, it would be more convenient to have a single index per frontend and apply the modulus on each log server in turn to see if the range has to be updated. It would then only perform one write per range switch. However the place where this is done doesn't have access to a frontend, so some changes would need to be performed for this, and it would require to update the current range independently in each logsrv, which is not necessarily easier since we don't know yet if we can commit it. |
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The HAProxy documentation has been split into a number of different files for ease of use. Please refer to the following files depending on what you're looking for : - INSTALL for instructions on how to build and install HAProxy - BRANCHES to understand the project's life cycle and what version to use - LICENSE for the project's license - CONTRIBUTING for the process to follow to submit contributions The more detailed documentation is located into the doc/ directory : - doc/intro.txt for a quick introduction on HAProxy - doc/configuration.txt for the configuration's reference manual - doc/lua.txt for the Lua's reference manual - doc/SPOE.txt for how to use the SPOE engine - doc/network-namespaces.txt for how to use network namespaces under Linux - doc/management.txt for the management guide - doc/regression-testing.txt for how to use the regression testing suite - doc/peers.txt for the peers protocol reference - doc/coding-style.txt for how to adopt HAProxy's coding style - doc/internals for developer-specific documentation (not all up to date)