[jira] Commented: (DERBY-2487) Enhance Derby with EXPLAIN Functionality

["Bryan Pendleton (JIRA)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/DERBY-2487?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12678240#action_12678240 ] 

Bryan Pendleton commented on DERBY-2487:
----------------------------------------

I intend to remove the 'NO_ACCESSED_HEAP_COLUMNS' column from
SYSXPLAIN_SCAN_PROPS. This column is always being set to NULL
in the current code, and I can't think of any use for this column which
isn't already being met by the NO_FETCHED_COLUMNS column.

It's possible that this field was intended to be used to hold the information
from an IndexRowToBaseRow result set, since
RealIndexRowToBaseRowStatistics does compute the columns accessed
from the base heap, and makes that information available in the text
output of the runtimestatistics. However, this result set does not have
a corresponding scan props row, so we don't have a way to hold
the value there. There is a commented-out bit of code in the
XPLAINSystemTableVisitor class which looks like it is intended to deposit
this information into the op_details column for the IndexRowToBaseRow
result set, which might be one way to make it available:

+        String op_details = "("+statistics.resultSetNumber + "), " + 
+                            statistics.tableName           ;//+ ", " +
+                            //"ACCESSED HEAP COLUMNS: "+ statistics.colsAccessedFromHeap;

For the time being, since I'm not sure what the column was supposed to
hold, and since having an always-NULL column doesn't seem useful,
I intend to remove the column from SCAN_PROPS.

> Enhance Derby with EXPLAIN Functionality
> ----------------------------------------
>
>                 Key: DERBY-2487
>                 URL: https://issues.apache.org/jira/browse/DERBY-2487
>             Project: Derby
>          Issue Type: New Feature
>          Components: SQL
>    Affects Versions: 10.2.2.0
>            Reporter: Felix Beyer
>            Assignee: Bryan Pendleton
>            Priority: Minor
>         Attachments: Derby physical XPLAIN schema.png, incorporateTrunkChanges.diff, removeSourceDepth.diff, RSProtocolNew.pdf, rts.xls, small logical xplain schema.pdf, startRegressionTest.diff, startRegressionTest.diff, startUpgradeTests.diff, updateRegressionTests.diff, updateRegressionTests.diff, usage.txt, xplain_patch_v1.txt, xplainClasses.pdf
>
>
> This enhancement extends Derby with EXPLAIN functions. Users want to have more feedback than they`re getting with the current RuntimeStatistics facility. This extension is based on the RuntimeStatistics/ResultSetStatistics functions / classes. 

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