Reduce memory by multiple GBs with many classic queues (backport #6684) #6795
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Store directory names as binary instead of string. This commit saves >1GB of memory per 100,000 classic queues v2. With longish node names, the memory savings are even much higher. This commit is especially a prerequisite for scalalbe MQTT where every subscribing MQTT connection creates its own classic queue. So, with 3 million MQTT subscribers, this commit saves >30 GB of memory. This commits stores file names as binaries and converts back to file:filename() when passed to file API functions. This is to reduce risk of breaking behaviour for path names containing unicode chars on certain platforms. Alternatives to the implementation in this commit: 1. Store common directory list prefix only once (e.g. put it into persistent_term) and store per queue directory names in ETS. 2. Use file:filename_all() instead of file:filename() and pass binaries to the file module functions. However this might be brittle on some platforms since these binaries are interpreted as "raw filenames". Using raw filenames requires more changes to classic queues which we want to avoid to reduce risk. The downside of the implemenation in this commit is that the binary gets converted to a list sometimes. This happens whenever a file is flushed or a new file gets created for example. Following perf tests did not show any regression in performance: ``` java -jar target/perf-test.jar -s 10 -x 1 -y 0 -u q -f persistent -z 30 java -jar target/perf-test.jar -s 10000 -x 1 -y 0 -u q -f persistent -z 30 java -jar target/perf-test.jar -s 10 -x 100 -qp q%d -qpf 1 -qpt 100 -y 0 -f persistent -z 60 -c 1000 ``` Furthermore `rabbit_file` did not show up in the CPU flame graphs either. (cherry picked from commit 8f0800e) # Conflicts: # deps/rabbit/src/rabbit_classic_queue_store_v2.erl # deps/rabbit/src/rabbit_variable_queue.erl
(cherry picked from commit b0d0308)
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This is an automatic backport of pull request #6684 done by Mergify.
Cherry-pick of 8f0800e has failed:
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