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https://issues.apache.org/jira/browse/ZOOKEEPER-965?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13037165#comment-13037165
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Ted Dunning commented on ZOOKEEPER-965:
---------------------------------------
{quote}
Ted, I'm not sure I understand what you mean by client-side insertion only. Can
you elaborate on what that would entail? Also, I'd be hesitant to do anything
that makes the server-side (or the C client) processing any more complex or
difficult than it already is....
{quote}
What I meant was that the rules for inserting place-holder results are pretty
simple. As such, if it is preferable to not return results from the server in
these spots, then a simple merge could be used to create a results list with
place-holder structures. Something like this:
{code}
Iterator<Result> i = results.iterator();
List<Result> r = Lists.newHashList();
for (op in ops) {
if (op.type() == CHECK) {
r.add(PLACE_HOLDER);
} else {
r.add(i.next());
}
}
{code}
I agree that complication of the client is bad, but this isn't much and if it
makes the server side easier, then it isn't a big deal. My guess is that the
server side solution is very simple (as in, just quit setting the version). Or
the cost of getting the version may be low enough we really don't care.
> 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, 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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