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https://issues.apache.org/jira/browse/ZOOKEEPER-965?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13028590#comment-13028590
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Marshall McMullen commented on ZOOKEEPER-965:
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The C client is just calling the new zoo_multi API. One of the unit tests does
a zoo_multi which purposefully fails (due to duplicate nodes). The error is
correctly detected and propagated from server back to client. The *NEXT* unit
tests which causes the server to start up again during it's init phase reads in
the database off of the disk (ZKDatabase.loadDatabase) which then ultimately
ends up in DataTree.processTxn(DataTree.java:818). That line of code is new
code I've added to processTxn that essentially says:
...
case OpCode.multi:
MultiTxn multiTxn = (MultiTxn) txn ;
List<Txn> txns = multiTxn.getTxns(); // <---- THAT CAUSES THE NULL
POINTER EXCEPTION B/C 'txn' is null.
So this bug only happens after a failed multi op. The normal multi op gets
written to disk and loaded correctly. I don't understand all of how this works,
but I presume we take a snapshot before we actually apply a transaction so we
can roll back if it fails. So I *think* the snapshot we're taking is putting a
null txn into the snapshot ... I'm not sure... Any ideas?
> 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
>
>
> 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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