rangefeed: add memory adjuster before publishing events #120348
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To prevent OOMs, we previously introduced memory budget to limit event buffering to processor.eventC channel. These events could point to large underlying data structure and keeping them in the channel prevent them from being garbage collected. However, the current memory accounting did not have a good way to predict the memory footprint of events. It uses calculateDateSize which 1. does not account for memory of the new RangeFeedEvents that could be spawned (such as checkpoint events) 2. inaccurately uses protobuf-encoded wire size for data 3. does not account for memory of the base structs. This patch improves the memory estimation by resolving the three points above. It tries its best effort to account for base struct's memory, predict generation of new events, and use actual data size rather than compressed protobuf size. Since it is challenging to predict whether there would be a new checkpoint event, our strategy in this PR is over-accounting >> under-accounting. GitHub issue (todo) tracks the remaining work to improve accuracy. Resolves: cockroachdb#114190 Release note: None
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We over-accounts at the beginning to account for everything that could have happened. If the memory turns out to be not needed, we de-allocates the memory right away to prevent registrations from holding onto unnecessary memory for too long.