[GitHub] [cassandra] yifan-c commented on a change in pull request #404: New/fql

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yifan-c commented on a change in pull request #404: New/fql
URL: https://github.com/apache/cassandra/pull/404#discussion_r372189193
 
 

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 File path: doc/source/new/fqllogging.rst
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+.. Licensed to the Apache Software Foundation (ASF) under one
+.. or more contributor license agreements.  See the NOTICE file
+.. distributed with this work for additional information
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+.. to you under the Apache License, Version 2.0 (the
+.. "License"); you may not use this file except in compliance
+.. with the License.  You may obtain a copy of the License at
+..
+..     http://www.apache.org/licenses/LICENSE-2.0
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+.. WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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+.. limitations under the License.
+
+Full Query Logging
+------------------ 
+
+Apache Cassandra 4.0 adds a new feature to support a means of logging all queries as they were invoked (`CASSANDRA-13983
+<https://issues.apache.org/jira/browse/CASSANDRA-13983>`_). For correctness testing it's useful to be able to capture production traffic so that it can be replayed against both the old and new versions of Cassandra while comparing the results.
+
+Cassandra 4.0 includes an implementation of a full query logging (FQL) that uses chronicle-queue to implement a rotating log of queries. Some of the features of FQL are:
+
+- Single thread asynchronously writes log entries to disk to reduce impact on query latency
+- Heap memory usage bounded by a weighted queue with configurable maximum weight sitting in front of logging thread
+- If the weighted queue is full producers can be blocked or samples can be dropped
+- Disk utilization is bounded by deleting old log segments once a configurable size is reached
+- The on disk serialization uses a flexible schema binary format (chronicle-wire) making it easy to skip unrecognized fields, add new ones, and omit old ones.
+- Can be enabled and configured via JMX, disabled, and reset (delete on disk data), logging path is configurable via both JMX and YAML
+- Introduce new ``fqltool`` in ``/bin`` that currently implements Dump which can dump in a readable format full query logs as well as follow active full query logs
 
 Review comment:
   The fql tool set now includes `Dump`, `Replay` and `Compare`.

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