Michael Semb Wever created CASSANDRA-21623:
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Summary: Report the number of rows replica filtering protection
cached when it warns
Key: CASSANDRA-21623
URL: https://issues.apache.org/jira/browse/CASSANDRA-21623
Project: Apache Cassandra
Issue Type: Improvement
Components: Consistency/Coordination
Reporter: Michael Semb Wever
Replica filtering protection warns when it caches more rows than
{{cached_replica_rows_warn_threshold}}:
{code}
Replica filtering protection has cached over 5 rows during query SELECT * FROM
ks.tbl WHERE v = 'old' LIMIT 9 ALLOW FILTERING. (See
'cached_replica_rows_warn_threshold' in cassandra.yaml.)
{code}
The message names the threshold, not the number of rows cached, so an operator
cannot tell a query that went one row over from one that went a thousand rows
over. The two need different responses: the first argues for raising the
threshold, the second for fixing the query.
The warning is also raised as the count crosses the threshold, which is before
the query reaches its high watermark, and the count the warning would want is
not known until the query ends.
The patch moves the warning to the end of the query, where {{maxRowsCached}} is
the high watermark the metric already records, and names that number:
{code}
Replica filtering protection has cached up to 6 rows during query SELECT * FROM
ks.tbl WHERE v = 'old' LIMIT 9 ALLOW FILTERING, which is over the warning
threshold of 5 rows defined by 'cached_replica_rows_warn_threshold' in
cassandra.yaml.
{code}
The failure message gains the count the same way. The failure threshold stays
on every increment, so an overloaded query still aborts at the row that crosses
it, and the warning is suppressed once the failure has fired, so one query
raises one message.
The {{hitWarningThreshold}} field goes away, and its comment with it: the
comment claimed the field tracked a partition, while nothing ever reset it, so
the warning was already once per query.
Patch:
[mck/upstream/rfp-cached-rows-warning/trunk|https://github.com/thelastpickle/cassandra/tree/mck/upstream/rfp-cached-rows-warning/trunk]
Provenance:
[b8bd9b19ce|https://github.com/datastax/cassandra/commit/b8bd9b19ce72c4f4d1f912ccc03fd62a59cbd2fc]
by [~adelapena]. That commit left a commented-out duplicate line in the test,
which this patch drops.
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