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From "Kim Haase (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (DERBY-5198) XPLAIN table documentation needs some cleanup
Date Tue, 19 Apr 2011 14:29:06 GMT

    [ https://issues.apache.org/jira/browse/DERBY-5198?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13021606#comment-13021606

Kim Haase commented on DERBY-5198:

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

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:
>            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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