Re: [Exist-open] Urgent assistance with locking behaviour of existdb / deadlocking

[Pieter L. <pie...@be...>]

Hi Adam,

It is not trivial to create a reproduceable case for the deadlocking 
problem but I am seeing deadlocks all the time when I do not take the 
necessary precautions when updating. I think it has to do with module 
imports. I think the deadlock occurs when the update of a library module 
is attempted which is also holding a read-lock because of an active 
process. Or the other way around: you make a request which involves a 
library which is being updated. At least one of these scenarios and 
maybe both can break my setup.

This does not seem to be Willem's problem tho.

Best,
Pieter

On 10/14/2025 9:59 AM, Adam Retter wrote:
>
> Hi Willem,
>
> In eXist-db 5.x.x and 6.x.x, the XQuery (if stored in the database) is 
> treated as any other document, and so it is locked for the duration of 
> operations that happen upon it. Unfortunately this means that whilst a 
> query is executing the document holding that query will keep a READ 
> lock on the document.
>
> A document may have many either a single write lock, or one or more 
> read locks. This means that the query can only be updated by one 
> person/client at a time, but that multiple clients can run the query 
> in parallel.
>
> I am not sure how a deadlock could occur with this. Can you provide 
> some further information about your issue, and how to reproduce it please?
>
> Thanks, Adam.
>
> On Tue, 14 Oct 2025 at 08:53, Willem van der Westhuizen 
> <wi...@kw...> wrote:
>
>     Hi
>
>     We use existdb extensively to run xqueries on our external databases,
>     couchdb and others. We dont use the existdb datastore for our data.
>
>     We used to run on an old 3.3.3 version of existdb, and recently
>     migrated
>     to 6.2. Since then we have found that existdb locks the xquery
>     that is
>     being executed, causing deadlocks that eventually locks up the
>     server.
>     Is there an easy way to tell existdb to revert to the older locking
>     behaviour that does not lock up the xquery being run?
>
>
>     Regards
>
>     -- 
>     Willem van der Westhuizen
>     +27 82 9200718
>
>
>
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>
>
>
> -- 
> Adam Retter
>
> eXist Core Developer
> { United Kingdom }
> ad...@ex...
>
>
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-- 
Pieter Lamers
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