Benoit Tellier created JAMES-3204:
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Summary: CassandraMessageMapper badly applies LIMIT
Key: JAMES-3204
URL: https://issues.apache.org/jira/browse/JAMES-3204
Project: James Server
Issue Type: Improvement
Components: cassandra, mailbox
Affects Versions: 3.5.0
Reporter: Benoit Tellier
Fix For: 3.6.0
We noticed some `BusyPool` exceptions filling up the driver queue upon IMAP
query (FETCH flags for all the messages in the mailbox).
The MessageManager do batch those reads (by default by 200 for metadata)., wich
then call the MessageMapper with this limit.
Some unit tests performed at the Cassandra mailbox level proved the soft
filtering did badly applies, and that we were performing uneeded extra reads
for the full batch read from the database.
One good mitigation strategy is to push the limit to the Cassandra query, and
ensures filtering happens before the extra reads are performed.
https://projectreactor.io/docs/core/release/api/reactor/core/publisher/Flux.html#take-long-
documents that it just don't propagate downstream request once a given amount
is reached however it do not ensure any form of backpressure. We might want to
further audit our code, looking for similar take mis-usages.
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