[Exist-open] FW: Is it possible to detect deadlocks in eXist?

[Jason S. <js...@in...>]

It looks like we have a deadlock.  Processor 15 is holding the lock that Processor 6 wants.  Processor 6 is holding the lock that processor 15 wants.  I was under the impression that you could have multiple, simultaneous read locks on a single collection.  Is that not true?  Can someone explain why read locks are deadlocking one another?

Jason Smith
________________________________________
From: Paul Ryan
Sent: Thursday, June 03, 2010 9:24 PM
To: Jason Smith
Subject: Re: [Exist-open] Is it possible to detect deadlocks in eXist?

You might want to forward this to the exist list as adam retter might be able to answer too.

-- Paul Ryan

On Jun 3, 2010, at 9:19 PM, Jason Smith wrote:

> Here is a JMX log.  These are all read locks.  I was under the impression that multiple threads could share many read locks, and that only write locks are blocking.  Was I mistaken?
>
> Thanks for your earlier answer.
>
> ******AFTER LOAD TEST (LOCKED STATE)
> Connected to MBean server.
> MEMORY:
> Current heap:       68,044 k        Committed memory:       103,616 k
> Max memory:        504,896 k
> List of threads currently waiting for a lock:
> -----------------------------------------------
> Thread http-8086-Processor17
>           Lock type: COLLECTION
>           Lock mode: READ
>             Lock id: /db
>             Held by: [http-8086-Processor6]
> Thread http-8086-Processor19
>           Lock type: COLLECTION
>           Lock mode: READ
>             Lock id: /db
>             Held by: [http-8086-Processor6]
> Thread http-8086-Processor12
>           Lock type: COLLECTION
>           Lock mode: READ
>             Lock id: /db
>             Held by: [http-8086-Processor6]
> Thread http-8086-Processor14
>           Lock type: COLLECTION
>           Lock mode: READ
>             Lock id: /db
>             Held by: [http-8086-Processor6]
> Thread http-8086-Processor15
>           Lock type: COLLECTION
>           Lock mode: READ
>             Lock id: /db
>             Held by: [http-8086-Processor6]
> Thread http-8086-Processor23
>           Lock type: COLLECTION
>           Lock mode: READ
>             Lock id: /db
>             Held by: [http-8086-Processor6]
> Thread http-8086-Processor4
>           Lock type: COLLECTION
>           Lock mode: READ
>             Lock id: /db
>             Held by: [http-8086-Processor6]
> Thread http-8086-Processor11
>           Lock type: COLLECTION
>           Lock mode: READ
>             Lock id: /db
>             Held by: [http-8086-Processor6]
> Thread http-8086-Processor8
>           Lock type: COLLECTION
>           Lock mode: READ
>             Lock id: /db
>             Held by: [http-8086-Processor6]
> Thread http-8086-Processor5
>           Lock type: COLLECTION
>           Lock mode: READ
>             Lock id: /db
>             Held by: [http-8086-Processor6]
> Thread http-8086-Processor6
>           Lock type: COLLECTION
>           Lock mode: READ
>             Lock id: /db/dashboard
>             Held by: [http-8086-Processor15]
>
>
> Jason Smith

> ________________________________________
> From: Wolfgang Meier [wol...@ex...]
> Sent: Thursday, June 03, 2010 4:17 PM
> To: Jason Smith
> Cc: ml
> Subject: Re: [Exist-open] Is it possible to detect deadlocks in eXist?
>
> Just a quick note (it's getting late here): you can use the JMX client
> (parameter -l) to obtain more information on which threads are
> currently waiting for locks on documents or collections and which
> other thread does hold that lock. See
>
> http://demo.exist-db.org/exist/jmx.xml#N10178
>
> It may help us to see the report this generates.
>
> Wolfgang