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When a cache is "cold" and multiple clients simultaneously try to access the same resource we must forward all the requests to the server. Next, every "duplicated" response will be processed in http_action_store_cache and we will try to cache every one of them regardless of whether this response was already cached. In order to avoid having multiple entries for a same primary key, the logic is then to first delete any preexisting entry from the cache tree before storing the current one. The actual previous response content will not be deleted yet though because if the corresponding row is detached from the "avail" list it might still be used by a cache applet if it actually performed a lookup in the cache tree before the new response could be received. This all means that we can end up using a valid row that references a cache_entry that was already removed from the cache tree. This does not pose any problem in regular caches (no 'vary' mechanism enabled) because the applet only works on the data and not the 'cache_entry' information, but in the "vary" context, when calling 'http_cache_applet_release' we might call 'delete_entry' on the given entry which in turn tries to iterate over all the secondary entries to find the right one in which the secondary entry counter can be updated. We would then call eb32_next_dup on an entry that was not in the tree anymore which ended up crashing. This crash was introduced by "48f81ec09 : MAJOR: cache: Delay cache entry delete in reserve_hot function" which added the call to "release_entry" in "http_cache_applet_release" that ended up crashing. This issue was raised in GitHub #2417. This patch must be backported to branch 2.9.
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)