Sophie Blee-Goldman created KAFKA-9062:
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Summary: RocksDB writes may stall after bulk loading lots of state
Key: KAFKA-9062
URL: https://issues.apache.org/jira/browse/KAFKA-9062
Project: Kafka
Issue Type: Bug
Components: streams
Reporter: Sophie Blee-Goldman
RocksDB may stall writes at times when background compactions or flushes are
having trouble keeping up. This means we can effectively end up blocking
indefinitely during a StateStore#put call within Streams, and may get kicked
from the group if the throttling does not ease up within the max poll interval.
Example: when restoring large amounts of state from scratch, we use the
strategy recommended by RocksDB of turning off automatic compactions and
dumping everything into L0. We do batch somewhat, but do not sort these small
batches before loading into the db, so we end up with a large number of
unsorted L0 files.
When restoration is complete and we toggle the db back to normal (not bulk
loading) settings, a background compaction is triggered to merge all these into
the next level. This background compaction can take a long time to merge
unsorted keys, especially when the amount of data is quite large.
Any new writes while the number of L0 files exceeds the max will be stalled
until the compaction can finish, and processing after restoring from scratch
can block beyond the polling interval
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