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[DOCS] Impala is not optimized for the IN operator when accessing HBASE

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Change-Id: I37337a18c7add3c64795b3b2e49670493a9a8e44
Reviewed-on: http://gerrit.cloudera.org:8080/14891
Reviewed-by: Lars Volker <lv@cloudera.com>
Tested-by: Impala Public Jenkins <impala-public-jenkins@cloudera.com>
This commit is contained in:
Alex Rodoni
2019-12-11 11:31:16 -08:00
parent 6bfa86faa0
commit acddf76bcb
1 changed files with 16 additions and 15 deletions
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31
docs/topics/impala_hbase.xml
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@@ -110,12 +110,12 @@ under the License.
the new table.)
</li>
<li>
You issue queries against the Impala tables. For efficient queries, use <codeph>WHERE</codeph> clauses to
find a single key value or a range of key values wherever practical, by testing the Impala column
corresponding to the HBase row key. Avoid queries that do full-table scans, which are efficient for
regular Impala tables but inefficient in HBase.
</li>
<li> You issue queries against the Impala tables. For efficient queries,
use the <codeph>WHERE</codeph> clause to find a single key value or a
range of key values wherever practical, by testing the Impala column
corresponding to the HBase row key. Avoid queries that do full-table
scans, which are efficient for regular Impala tables but inefficient
in HBase. </li>
</ul>
<p>
@@ -180,15 +180,16 @@ under the License.
key or value fields. All the type enforcement is done on the Impala side.
</p>
<p>
For best performance of Impala queries against HBase tables, most queries will perform comparisons in the
<codeph>WHERE</codeph> against the column that corresponds to the HBase row key. When creating the table
through the Hive shell, use the <codeph>STRING</codeph> data type for the column that corresponds to the
HBase row key. Impala can translate conditional tests (through operators such as <codeph>=</codeph>,
<codeph>&lt;</codeph>, <codeph>BETWEEN</codeph>, and <codeph>IN</codeph>) against this column into fast
lookups in HBase, but this optimization (<q>predicate pushdown</q>) only works when that column is
defined as <codeph>STRING</codeph>.
</p>
<p> For best performance of Impala queries against HBase tables, most
queries will perform comparisons in the <codeph>WHERE</codeph> clause
against the column that corresponds to the HBase row key. When creating
the table through the Hive shell, use the <codeph>STRING</codeph> data
type for the column that corresponds to the HBase row key. Impala can
translate predicates (through operators such as <codeph>=</codeph>,
<codeph>&lt;</codeph>, and <codeph>BETWEEN</codeph>) against this
column into fast lookups in HBase, but this optimization (<q>predicate
pushdown</q>) only works when that column is defined as
<codeph>STRING</codeph>. </p>
<p>
Starting in Impala 1.1, Impala also supports reading and writing to columns that are defined in the Hive