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From Pavel Bortnovskiy <pbortnovs...@jefferies.com>
Subject RE: Derby Locks - best practices
Date Fri, 01 Jun 2012 19:50:42 GMT
Hello, David, thanks for your quick response.

Usually it's one thread "per" in-memory table. Tables can be updated at random times and their
random rows may be updated, some rows deleted or new rows inserted. In some other configuration,
to avoid deletions, updates and inserts, the in-memory table is truncated and then all the
records (the new "state" of the source data) are inserted into it.

The thread which runs SQL against all those tables frequently may do a scan of the whole table.

-----Original Message-----
From: David Zanter [mailto:dzanter@gmail.com]
Sent: Friday, June 01, 2012 3:46 PM
To: Derby Discussion
Subject: Re: Derby Locks - best practices

Do mean the scenario of:
    Multiple threads are updating the exact same rows

or
    Multiple threads doing updates to different rows, but due to queries/indexes/etc are causing
contention between each other.

On Fri, Jun 1, 2012 at 3:16 PM, Pavel Bortnovskiy <pbortnovskiy@jefferies.com> wrote:
> Hello, all:
>
>
>
> Derby is used in my application in the in-memory only mode. For a long
> time Derby's lock logic caused no worries, but recently some use cases
> failed with lock timeouts. Thus I'm looking for guidance on best
> practices for handling locks in Derby. A use-case which may cause
> timeouts to obtain a
> lock: one thread is executing an SQL statement which accesses two (or
> more) in-memory tables. Those two tables are being modified by  other
> threads at random times. So, situations in which the SQL is executed
> for a long time and the other threads are frequently updating the
> tables may cause lock timeouts.
>
>
>
> Besides best practices to avoid timeouts and deadlocks, I would like
> to ask the following questions:
>
> 1)      What's the default length of lock timeouts?
>
> 2)      Does my app need another layer of synchronization
> mechanism/locks to avoid attempts to update in-memory tables or execute SQLs against
them?
>
> 3)      Can my application utilize Derby's locks through some API - to
> query their state or to use them in making a decision of whether to
> batch updates or to execute them, to wait or execute the SQLs?
>
>
>
> Your help would be greatly appreciated,
>
>
>
> Pavel.
>
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or otherwise use it or any part of it in any form whatsoever. This email may be produced at
the request of regulators or in connection with civil litigation. Jefferies accepts no liability
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