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https://issues.apache.org/jira/browse/CASSANDRA-3303?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13142194#comment-13142194
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Sylvain Lebresne commented on CASSANDRA-3303:
---------------------------------------------
On the patch, a few minor remarks:
* There is a weird UnImplNode on top of ReadCommand.java (that prevents
compilation)
* I think we could replace isLongRead and trimLongRead by a maybeTrim() method
that would be a noop by default. Basically trimLongRead requires that
isLongRead() has been called (otherwise it throws an unsupported exception), so
in those case I think it's easier to use if it's just one method. Same for the
pair (isShortRead, generateShortRetry) actually.
* nit: There is some imports rewrite (java.io.* -> multiple imports) in SFRC.
It's a big deal but that kind of thing makes diffs bigger than necessary so
it's nice to take the habit to no do that.
Now I don't think this patch addresses CASSANDRA-3395 as is. For that, we would
basically need to move the trimLongRead to SliceFromReadCommand directly (the
bug of CASSANDRA-3395 is that normal SliceFromReadCommand can have more that
requested columns because of reconciliation of the result of different nodes).
The easiest way here is probably to move the trim code to a
SliceFromReadCommand.maybeTrim() and to have that method uses some
getRequestedCount() method. For SFRC, the latter method would return count, for
RSFRC, it would return originalCount.
> Short reads protection results in returning more columns than asked for
> -----------------------------------------------------------------------
>
> Key: CASSANDRA-3303
> URL: https://issues.apache.org/jira/browse/CASSANDRA-3303
> Project: Cassandra
> Issue Type: Bug
> Components: Core
> Affects Versions: 1.0.0
> Reporter: Sylvain Lebresne
> Assignee: Byron Clark
> Priority: Minor
> Fix For: 1.0.2
>
> Attachments: cassandra-3303-1.patch, cassandra-3303-2.patch,
> cassandra-3303-3.patch, cassandra-3303-4.patch, long_read.sh
>
>
> When we detect a short read (in SP.fetchRows), we retry a new command created
> by:
> {noformat}
> logger.debug("detected short read: expected {} columns, but only resolved {}
> columns", sliceCommand.count, liveColumnsInRow);
> int retryCount = sliceCommand.count + sliceCommand.count - liveColumnsInRow;
> SliceFromReadCommand retryCommand = new SliceFromReadCommand(command.table,
> command.key,
>
> command.queryPath,
>
> sliceCommand.start,
>
> sliceCommand.finish,
>
> sliceCommand.reversed,
> retryCount);
> {noformat}
> That is, in that new command, the count is greater than what asked in the
> initial command. But we never cut back the result of that new retried query.
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