Github user DaveBirdsall commented on a diff in the pull request:
https://github.com/apache/incubator-trafodion/pull/379#discussion_r56197806
--- Diff: docs/cqd_reference/src/asciidoc/_chapters/query_execution.adoc ---
@@ -0,0 +1,239 @@
+////
+/**
+* @@@ START COPYRIGHT @@@
+*
+* 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
+* regarding copyright ownership. The ASF licenses this file
+* to you under the Apache License, Version 2.0 (the
+* "License"); you may not use this file except in compliance
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+*
+* http://www.apache.org/licenses/LICENSE-2.0
+*
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+*
+* @@@ END COPYRIGHT @@@
+ */
+////
+
+[[query-execution]]
+= Query Execution
+
+This section describes CQDs that are used to influence query execution.
+
+[[hbase-async-operation]]
+== HBASE_ASYNC_OPERATION
+
+[cols="25%h,75%"]
+|===
+| *Description* | Allows index maintenance to be performed
concurrently with base table operation.
+| *Values* | *'ON'* Index maintenance is allowed. +
+*'OFF'* Index maintenance is not allowed. +
+ +
+The default value is *'ON'*.
+| *Usage* | HBase `put` operations are blocking. When
the table has one or more indexes,
+then the insert/update/delete (IUD) operation response time is improved by
executing the index maintenance
+operations concurrently with the base table operation: the put operations
to these HBase tables are executed
+in different threads.
+| *Production Usage* | Yes. It is 'ON' by default. This feature
can be disabled by setting this CQD to 'OFF'.
+| *Impact* | IUD operations on tables with one or more
indexes can become slower.
+| *Level* | Query.
+| *Conflicts/Synergies* | Not applicable.
+| *Real Problem Addressed* | Not applicable.
+| *Introduced In Release* | Trafodion 1.3.0.
+| *Deprecated In Release* | Not applicable.
+|===
+
+<<<
+[[hbase-cache-blocks]]
+== HBASE_CACHE_BLOCKS
+
+[cols="25%h,75%"]
+|===
+| *Description* | Influences HBase to retain the data blocks
in memory after they are read.
+| *Values* |
+*'ON'/'OFF'/'SYSTEM'* +
+ +
+The default value is *'SYSTEM'*.
+| *Usage* | HBase maintains the block cache structure
to retain the data blocks in memory after they are read.
+In LRU block cache configuration, the amount of block cache retained in
memory is proportional to the amount of reserved maximum
+Java heap size of the region server. LRU Block Cache is the default in
HBase. +
+ +
+The Trafodion Optimizer determines whether a sequential scan of the HBase
table in a query would cause the full eviction of the
+data blocks cached earlier thereby impacting the performance of the random
reads. The cache blocks option is turned off for the table
+in such a case. +
+ +
+Set the CQD
<<hbase-region-server-max-heap-size,HBASE_REGION_SERVER_MAX_HEAP_SIZE>> value
to reflect the amount of java heap size reserved for the region servers.
+This CQD is used by the Trafodion Optimizer to evaluate if the block cache
to be turned off.
--- End diff --
Suggested wordsmith: "This CQD is used by the Trafodion Optimizer to decide
if the block cache should be turned off."
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