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https://issues.apache.org/jira/browse/DERBY-4741?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12922096#action_12922096
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Dag H. Wanvik edited comment on DERBY-4741 at 10/18/10 11:06 AM:
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Thanks for doing more measurements, Knut! It seems that even in the best case,
the movePostion operation is negatively impacted with 1-2% due to the
ThreadLocal access, which is not desirable.
Knut mentioned that ContextService is already based on a ThreadLocal. I checked
around a bit and found that we might be able to get rid of the InterruptStatus
thread local check in the API methods in this way:
If we were able to retrieve the lcc at the point where we detect the interrupts
and save this fact in the lcc at that time, the cost of accessing a ThreadLocal
variable would not be incurred unless AN INTERRUPT ACTUALLY HAPPENED.
In the API methods, lcc is already available, and checking a boolean flag in
the lcc instead of calling InterruptStatus#throwIf (which accesses a thread
local) would be much cheaper. I see we already sometimes do dig out the lcc in
store level code, e.g. in store.access.DiskHashtable, in this way:
LanguageConnectionContext lcc = (LanguageConnectionContext)
ContextService.getContextOrNull( // this call accesses a
ThreadLocal
LanguageConnectionContext.CONTEXT_ID);
I'll look into this approach a bit.
was (Author: dagw):
Thanks for doing more measurements, Knut! It seems that even in the best
case, the movePostion operation is negatively impacted with 1-2% due to the
ThreadLocal access, which is not desirable.
Knut mentioned that ContextService is already based on a ThreadLocal. I checked
around a bit and found that we might be able to get rid of the InterruptStatus
thread local check in the API methods in this way:
If we were able to retrieve the lcc at the point where we detect the interrupts
and save this fact in the lcc at that time, the cost of accessing a ThreadLocal
variable would not be incurred unless AN INTERRUPT ACTUALLY HAPPENED.
In the API methods, lcc is already available, and checking a boolean flag in
lthe cc instead of calling InterruptStatus#throwIf (which accesses a thread
local) would be much cheaper. I see we already sometimes do dig out the lcc in
store level code, e.g. in store.access.DiskHashtable, in this way:
LanguageConnectionContext lcc = (LanguageConnectionContext)
ContextService.getContextOrNull( // this call accesses a
ThreadLocal
LanguageConnectionContext.CONTEXT_ID);
I'll look into this approach a bit.
> Make Derby work reliably in the presence of thread interrupts
> -------------------------------------------------------------
>
> Key: DERBY-4741
> URL: https://issues.apache.org/jira/browse/DERBY-4741
> Project: Derby
> Issue Type: Bug
> Components: Store
> Affects Versions: 10.2.1.6, 10.2.2.0, 10.3.1.4, 10.3.2.1, 10.3.3.0,
> 10.4.1.3, 10.4.2.0, 10.5.1.1, 10.5.2.0, 10.5.3.0, 10.6.1.0
> Reporter: Dag H. Wanvik
> Assignee: Dag H. Wanvik
> Attachments: derby-4741-nio-container+log+waits+locks+throws.diff,
> derby-4741-nio-container+log+waits+locks+throws.stat,
> derby-4741-nio-container+log+waits+locks-2.diff,
> derby-4741-nio-container+log+waits+locks-2.stat,
> derby-4741-nio-container+log+waits+locks.diff,
> derby-4741-nio-container+log+waits+locks.stat,
> derby-4741-nio-container+log+waits.diff,
> derby-4741-nio-container+log+waits.stat, derby-4741-nio-container+log.diff,
> derby-4741-nio-container+log.stat, derby-4741-nio-container-2.diff,
> derby-4741-nio-container-2.log, derby-4741-nio-container-2.stat,
> derby-4741-nio-container-2b.diff, derby-4741-nio-container-2b.stat,
> derby.log, derby.log, MicroAPITest.java, xsbt0.log.gz
>
>
> When not executing on a small device VM, Derby has been using the Java NIO
> classes java.nio.clannel.* for file io.
> If thread is interrupted while executing blocking IO operations in NIO, the
> ClosedByInterruptException will get thrown. Unfortunately, Derby isn't
> current architected to retry and complete such operations (before passing on
> the interrupt), so the Derby database can be left in an inconsistent state
> and we therefore have to return a database level error. This means the
> applications can no longer access the database without a shutdown and reboot
> including a recovery.
> It would be nice if Derby could somehow detect and finish IO operations
> underway when thread interrupts happen before passing the exception on to the
> application. Derby embedded is sometimes embedded in applications that use
> Thread.interrupt to stop threads.
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