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https://issues.apache.org/jira/browse/ZOOKEEPER-965?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13034593#comment-13034593
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Marshall McMullen commented on ZOOKEEPER-965:
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Benjamin,
Thanks very much!! This was a lot of work, but also very interesting. Really
glad to have been able to jump in and work on it. As to your questions:
1) Yes, if there is an error in any of the ops in the multi-op, then the entire
multi-op fails. On the java client, this will throw an exception corresponding
to the error in the op that caused the multi-op to fail. You also optionally
get an array populated with the results of each op in the multi-op in case you
want to iterate over it and see which one failed. The semantics of the error
codes in that result array are as follows
ZOK: the op would have succeeded
ZRUNTIMEINCONSISTENCY: We never tried the op because it was *after* the op that
caused the multi-op to fail. I chose this error code (somewhat arbitrarily)
because it would violate transactional consistency if we were to have committed
an op inside a failing multi-op.
Anything else: The error of the failing op.
2) Ted, feel free to jump in here, but I believe the idea is to not proceed
with the ops that follow in a multi op if a version on some other node has
changed out from under us. e.g. if you have 100 ops in a multi op, and you get
to the 50th one, it's a way to do a sanity check of "hey, don't go past this
point if any other client changed this node"... Does that make sense?
> Need a multi-update command to allow multiple znodes to be updated safely
> -------------------------------------------------------------------------
>
> Key: ZOOKEEPER-965
> URL: https://issues.apache.org/jira/browse/ZOOKEEPER-965
> Project: ZooKeeper
> Issue Type: Bug
> Affects Versions: 3.3.3
> Reporter: Ted Dunning
> Assignee: Ted Dunning
> Fix For: 3.4.0
>
> Attachments: ZOOKEEPER-965.patch, ZOOKEEPER-965.patch,
> ZOOKEEPER-965.patch, ZOOKEEPER-965.patch, ZOOKEEPER-965.patch,
> ZOOKEEPER-965.patch, ZOOKEEPER-965.patch, ZOOKEEPER-965.patch,
> ZOOKEEPER-965.patch, ZOOKEEPER-965.patch, ZOOKEEPER-965.patch,
> ZOOKEEPER-965.patch
>
>
> The basic idea is to have a single method called "multi" that will accept a
> list of create, delete, update or check objects each of which has a desired
> version or file state in the case of create. If all of the version and
> existence constraints can be satisfied, then all updates will be done
> atomically.
> Two API styles have been suggested. One has a list as above and the other
> style has a "Transaction" that allows builder-like methods to build a set of
> updates and a commit method to finalize the transaction. This can trivially
> be reduced to the first kind of API so the list based API style should be
> considered the primitive and the builder style should be implemented as
> syntactic sugar.
> The total size of all the data in all updates and creates in a single
> transaction should be limited to 1MB.
> Implementation-wise this capability can be done using standard ZK internals.
> The changes include:
> - update to ZK clients to all the new call
> - additional wire level request
> - on the server, in the code that converts transactions to idempotent form,
> the code should be slightly extended to convert a list of operations to
> idempotent form.
> - on the client, a down-rev server that rejects the multi-update should be
> detected gracefully and an informative exception should be thrown.
> To facilitate shared development, I have established a github repository at
> https://github.com/tdunning/zookeeper and am happy to extend committer
> status to anyone who agrees to donate their code back to Apache. The final
> patch will be attached to this bug as normal.
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