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From "Ted Dunning (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (ZOOKEEPER-965) Need a multi-update command to allow multiple znodes to be updated safely
Date Fri, 20 May 2011 23:55:47 GMT

    [ https://issues.apache.org/jira/browse/ZOOKEEPER-965?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13037165#comment-13037165
] 

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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