Github user DaveBirdsall commented on a diff in the pull request:
https://github.com/apache/incubator-trafodion/pull/379#discussion_r56198719
--- 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
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+ */
+////
+
+[[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.
+| *Production Usage* | Leave the setting to be 'SYSTEM' when
HBase is configured to use LRU block cache. If needed,
+you can override this settings with 'ON' or 'OFF'. +
+ +
+With other HBase configurations, you need to set HBASE_CACHE_BLOCKS to
'ON' or 'OFF' based on your application needs.
+| *Impact* | Automatically retains the random read
performance.
+| *Level* | Query.
+| *Conflicts/Synergies* | Not applicable.
+| *Real Problem Addressed* | Not applicable.
+| *Introduced In Release* | Trafodion 1.3.0.
+| *Deprecated In Release* | Not applicable.
+|===
+
+<<<
+[[hbase-filter-preds]]
+== HBASE_FILTER_PREDS
+
+[cols="25%h,75%"]
+|===
+| *Description* | Allows push down of predicates to HBase
Region Servers using HBase filters and optimize the columns retrieved
+from Region Servers. Only supported for NON ALIGN FORMAT tables.
+| *Values* |
+*'OFF'*: Predicates are never pushed down. +
+*'ON'*: A first implementation targeted for deprecation is enabled.
Support simple predicate formed by a combination of AND only.
+Could be counter-productive when applied on nullable columns. +
+*'1'*: Same as *'ON'*. +
+*'2'*: Full feature is enabled. +
+ +
+An explain plan can show whether predicates are successfully pushed down
to the Region Servers and what columns are really retrieved. +
+ +
+The default value is *'OFF'*.
+| *Usage* | Used to improve performance by reducing
the number of columns retrieved to a strict minimum
+and filter out rows as early as possible.
+| *Production Usage* | Please consult the Trafodion community.
+| *Impact* | Using this CQD increases the amount of
work done in the HBase Region Servers.
+| *Level* | System or Session.
+| *Conflicts/Synergies* | Not applicable.
+| *Real Problem Addressed* | Not applicable.
+| *Introduced In Release* | Trafodion 2.0.0.
+| *Deprecated In Release* | Not applicable.
+|===
+
+<<<
+[[hbase-hash2-partitioning]]
+== HBASE_HASH2_PARTITIONING
+
+[cols="25%h,75%"]
+|===
+| *Description* | Treat salted Trafodion tables as
hash-partitioned on the salt columns.
+| *Values* |
+*'OFF'*: Salted Trafodion tables are not hash-partitioned on the salt
columns. +
+*'ON'*: Salted Trafodion tables are hash-partitioned on the salt columns. +
+ +
+The default value is *'ON'*.
+| *Usage* | If, for any reason, there are issues with
parallel plans on salted tables (especially with data skew) then try setting
this CQD to OFF.
+| *Production Usage* | Yes.
+| *Impact* | Not applicable.
+| *Level* | System or Session.
+| *Conflicts/Synergies* | Not applicable.
+| *Real Problem Addressed* | Not applicable.
+| *Introduced In Release* | Trafodion 2.0.0.
+| *Deprecated In Release* | Not applicable.
+|===
+
+<<<
+[[hbase_num_cache_rows_max]]
+== HBASE_NUM_CACHE_ROWS_MAX
+
+[cols="25%h,75%"]
+|===
+| *Description* | Determines the number of rows obtained
from HBase in one RPC call to the HBase Region Server in a sequential scan
operation,
+| *Values* |
+Numeric value. +
+ +
+The default value is *'10000'*.
+| *Usage* | This CQD can be used to tune the query to
perform optimally by reducing the number of interactions to the HBase Region
Servers during
+a sequential scan of a table. +
+ +
+You need to consider how soon the maximum number of rows are materialized
on the Region Servers. When filtering is pushed down to Region Servers,
+then it can take a longer time depending upon the query and the predicates
involved. This can result in HBase scanner timeouts.
+| *Production Usage* | Use the default setting and reduce the
value to avoid HBase scanner timeouts. Consult with the Trafodion community
+if you think that you need to use this CQD.
+| *Impact* | Not applicable.
+| *Level* | Query.
+| *Conflicts/Synergies* | Not applicable.
+| *Real Problem Addressed* | Not applicable.
+| *Introduced In Release* | Trafodion 1.3.0.
+| *Deprecated In Release* | Not applicable.
+|===
+
+<<<
+[[hbase-rowset-vssb-opt]]
+== HBASE_ROWSET_VSSB_OPT
--- End diff --
Typo. Should be HBASE_ROWSET_VSBB_OPT
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