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From "Tyler Hobbs (JIRA)" <>
Subject [jira] [Commented] (CASSANDRA-9304) COPY TO improvements
Date Fri, 13 Nov 2015 19:26:11 GMT


Tyler Hobbs commented on CASSANDRA-9304:

Great, thanks for taking care of the windows problems!  Here are some review comments on the
current patch:

In {{write_rows_to_csv()}}, instead of using {{sys.exec_info()\[0\]}}, it seems like we could
just use the caught exception (by doing {{except Exception, e:}}).  Am I missing a reason
why that won't work here?

In {{get_ranges()}}, this line will result in two token ranges using the same dict, so the
count of attempts and rows can become incorrect:
ranges[(previous, None)] = ranges[(previous_previous, previous)]

Just using {{.copy()}} on the dict should be fine.

In {{report_error()}}, the {{issubclass()}} check should be {{isinstance()}} instead.

If a child process dies, we don't (and can't) make any adjustments to the {{suceeded}}/{{failed}}
count.  Because the jobs that were queued to that process aren't resubmitted, this results
in the copy process looping endlessly.  I see two possible solutions:
# Track which token ranges we've submitted to each process.  When a child process dies, re-submit
any of those token ranges for which we have 0 rows.
# Error the entire copy process

I'm personally okay with option #2, so feel free to go with that if you don't want to do the
work for #1.

I was able to find these bugs by editing the code to some simple fault injection in {{start_job()}}:
if random.random() > 0.7:
   future = session.execute_async("SELECT * FROM badtable")                              
elif random.random() > 0.99:                                                          
    future = session.execute_async(query)            
I think it would be a good idea to expose something like this for testing through an environment
variable.  That would allow us to easily exercise these different error scenarios in dtests
that are otherwise hard to replicate.

Overall, though, I'm a big fan of this patch.  You've done excellent work on this so far.

> COPY TO improvements
> --------------------
>                 Key: CASSANDRA-9304
>                 URL:
>             Project: Cassandra
>          Issue Type: Improvement
>            Reporter: Jonathan Ellis
>            Assignee: Stefania
>            Priority: Minor
>              Labels: cqlsh
>             Fix For: 2.1.x, 2.2.x, 3.x
> COPY FROM has gotten a lot of love.  COPY TO not so much.  One obvious improvement could
be to parallelize reading and writing (write one page of data while fetching the next).

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