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https://issues.apache.org/jira/browse/DERBY-5198?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13021606#comment-13021606
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Kim Haase commented on DERBY-5198:
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I've listed the issues with the XPLAIN system table docs below, along with some
possible solutions if they seem obvious.
rrefsysxplain_statements.dita, STMT_NAME row:
"The name of the associated query or statement. This value is NULL if the user
did not assign a name. I'm not sure how the user assigns a name to a statement,
perhaps by calling Statement.setCursorName()?"
Do we know the answer to this? Otherwise, I can just remove the question.
rrefsysxplain_resultsets.dita, OP_IDENTIFIER row:
"A code indicating what type of result set these statistics are for. Common
result set types include: TABLESCAN, INDEXSCAN, PROJECTION, etc. Should I try
to list all the result set types here?"
Are the names easy to find somewhere? (I can't find them, but that means
little.) If not, they should be listed; if so, the examples are fine.
rrefsysxplain_resultsets.dita, DEFERRED_ROWS row:
"The column is only non-null for INSERT, UPDATE, and DELETE result sets. For
those result sets, this column holds 'Y' if the INSERT/UPDATE/DELETE is
being performed using deferred change semantics, and holds 'N' otherwise. I
think that deferred change semantics are used when there is self-referencing
going on, and we must avoid the "Halloween" problem of processing the rows
multiple times."
Can "I think that" be removed? More rephrasing might be helpful.
rrefsysxplain_resultset_timings.dita, TEMP_CONG_CREATE_TIME row:
"For result sets which involve a materialization of a temporary intermediate
result set, this value is the time it took to create the materialized result
set, in milliseconds. I think this may occur with hash joins where the number
of rows in the intermediate result is too large to hold in memory?"
Can "I think" be removed?
rrefsysxplain_scan_props.dita, FETCH_SIZE row:
"I think this is the number of pages fetched at a time when the scan is
retrieving pages from disk? I expected this to be 16 when doing a TABLESCAN,
and 1 when doing an INDEXSCAN, but I've also seen it be 16 for INDEXSCAN?"
Can this be changed to just "The number of pages fetched at a time when the
scan is retrieving pages from disk"?
rrefsysxplain_sort_props.dita, SORT_TYPE row:
"A code indicating the type of sort that was performed. The code values include
'IN' for an internal sort, and 'EX' for an external sort. I think that an
internal sort is one which was entirely performed in-memory and did not
overflow to any temporary files, while an external sort used one or more
external files."
Can "I think that" be removed?
> XPLAIN table documentation needs some cleanup
> ---------------------------------------------
>
> Key: DERBY-5198
> URL: https://issues.apache.org/jira/browse/DERBY-5198
> Project: Derby
> Issue Type: Bug
> Components: Documentation
> Affects Versions: 10.7.1.1
> Reporter: Kim Haase
> Assignee: Kim Haase
> Priority: Minor
>
> While working on DERBY-5184 (table cleanup), I noticed that in some of the
> XPLAIN style tables topics there remain some questions that were not answered
> by reviewers and that managed to make it into the final documentation. These
> should be fixed separately from DERBY-5184, which focuses on formatting
> rather than substantive questions.
> I'll list the problems in a comment.
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