Fix memory leak in subscription "message-id to topic" mapping #1535
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robertsLando
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Nov 14, 2022
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@YoDaMa ping |
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@vishnureddy17 @ryanwinter @BertKleewein anyone here that can kindly merge this PR? |
vishnureddy17
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…1622) @vishnureddy17 Fix typo in README 00bf657 @bverhoeven Fix memory leak in subscription topic mapping (#1535) 8c77eec @mwohlert @robertsLando @ynagasaki feat: allow user to disable pre-generated write cache (#1151) 0d11888 Co-authored-by: Daniel Lando <[email protected]> Co-authored-by: Yoshi Nagasaki <[email protected]> Co-authored-by: Dmitry Kurmanov <[email protected]> Co-authored-by: Vishnu Reddy <[email protected]> Co-authored-by: Bas Verhoeven <[email protected]> Co-authored-by: Michel Wohlert <[email protected]>
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We've been using this library extensively in a project that makes a lot of subscriptions and have noticed that it's been leaking memory (which is causing NodeJS to crash with "JavaScript heap out of memory").
We've pinpointed this to the MQTT.js library's "message id to subscription" mapping:
A message ID is assigned and stored in
messageIdToTopicwhenever a new subscription is started and resubscription is enabled (which is the default). The message-id to topic mapping is never cleared and keeps accumulating over time, which creates a memory leak that can not be resolved by the caller.This mapping seems to have been introduced as a way to prevent resubscriptions of topics that have failed to subscribe on their first attempt, as introduced in as part of #665 in f6d12f0
There's, unless I'm overlooking something, no reason to keep this mapping in place once an acknowledgement is received. With that assumption, I've created a few tests to reproduce the issue and have created a simple fix that clears the mapping when
SUBACKis received.We've been running a patched version of the library and have noticed a significant reduce in memory usage and can confirm that, for us, the memory leak has been resolved. Would love to get this included upstream though. If there's something that we missed, I'd love to know too!