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From DaveBirdsall <>
Subject [GitHub] incubator-trafodion pull request: Trafodion 1851: Publication of n...
Date Tue, 15 Mar 2016 16:49:22 GMT
Github user DaveBirdsall commented on a diff in the pull request:
    --- 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
    +* with the License.  You may obtain a copy of the License at
    +* Unless required by applicable law or agreed to in writing,
    +* software distributed under the License is distributed on an
    +* KIND, either express or implied.  See the License for the
    +* specific language governing permissions and limitations
    +* under the License.
    +* @@@ END COPYRIGHT @@@
    +  */
    += Query Execution
    +This section describes CQDs that are used to influence query execution.
    +| *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.
    +| *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
    --- 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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