[GitHub] keith-turner commented on a change in pull request #100: Add docs for scan execution hints apache/accumulo#571

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keith-turner commented on a change in pull request #100: Add docs for scan execution hints apache/accumulo#571
URL: https://github.com/apache/accumulo-website/pull/100#discussion_r206860929
 
 

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 File path: _docs-2-0/administration/scan-executors.md
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 @@ -104,11 +104,41 @@ executor.
 
 ```
 tserver.scan.executors.default.prioritizer=org.apache.accumulo.core.spi.scan.IdleRatioScanPrioritizer
-```  
+```
 
 Using the IdleRatioScanPrioritizer in a test with 50 long running scans and 5
 threads repeatedly doing small random lookups made a significant difference.
-In this test the average lookup time for the 5 threads went from 250ms to 5 ms.  
+In this test the average lookup time for the 5 threads went from 250ms to 5 ms.
+
+### Providing hints from the client side.
+
+Scanners can provide hints to ScanDispatchers and ScanPriotizers by calling
+[setExecutionHints] on the Scanner.  What, if anything, is done with these
+hints depends on what is configured for the table and system.  Accumulo's
+default configuration ignores hints. The following shell commands make it
+possible to choose an executor and set priorities from a scanner for the
+table `tex`.
+
+```
+config -s tserver.scan.executors.special.threads=8
+config -s tserver.scan.executors.special.prioritizer=org.apache.accumulo.core.spi.scan.HintScanPrioritizer
+createtable tex
+config -t tex -s table.scan.dispatcher.opts.heed_hints=true
+```
+
+The {% jlink org.apache.accumulo.core.spi.scan.HintScanPrioritizer %} honors
+hints of the form `priority=<integer>` to prioritize scans, with lower integers
+resulting in a higher priority. The `SimpleScanDispatcher`, which is the
+default dispatcher, supports the `heed_hints` option. By default the
+`SimpleScanDispatcher` ignores hints, but when `heed_hints` is set to `true` it
+will honor hints of the form `executor=<executor name>` when choosing an
 
 Review comment:
   `table.scan.dispatcher` defaults to `org.apache.accumulo.core.spi.scan.SimpleScanDispatcher` which is why only `heed_hints` can be set.   Its probably safer to set it though.

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