[ZODB-Dev] "Transaction blocked waiting for storage"

[Andreas Jung]

On 22.06.09 17:37, Jim Fulton wrote:
>
> On Jun 22, 2009, at 11:31 AM, Alan Runyan wrote:
>
>> On Mon, Jun 22, 2009 at 10:06 AM, Andreas Jung<lists at zopyx.com> wrote:
>>> On 22.06.09 16:56, Pedro Ferreira wrote:
>>>> Hello all,
>>>> We occasionally get some messages like this in the logs:
>>>>
>>>> 2009-06-22T14:12:42 (30651/137.138.128.213:35787) Transaction blocked
>>>> waiting for storage. Clients waiting: 1.
>>>>
>>>> But today we eventually got to:
>>>>
>>>> 2009-06-22T16:00:11 (30651/137.138.4.153:53416) Transaction blocked
>>>> waiting for storage. Clients waiting: 204.
>>>>
>>>> Which lasted some minutes.  During that time, our system seemed to
>>>> hang,
>>>> even if it was possible to connect to the db through the command line.
>>>> It eventually went back to normal by itself.
>>>> Any clue on what might have caused this?
>>> The reason is likely a long running transaction. Since the storage
>>> server
>>> is single-threaded, a long running transaction will block pending
>>> requests.
>>
>> Question:
>> Will the ZEO server respond to LOAD requests from ZEO clients while
>> WRITEs are pending?
>
>
> Yes, however, if the last phase of 2-phase commit takes long enough,
> clients will become blocked altogether.  This is because vote requests
> get blocked and eventually, all of the client threads are blocked voting.
I think Dieter's patch is related to this issue:

https://bugs.launchpad.net/zodb/+bug/373625

Andreas
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