[ http://issues.apache.org/jira/browse/DERBY-733?page=all ]
Knut Anders Hatlen updated DERBY-733:
-------------------------------------
Attachment: DERBY-733-more-exception-handling.diff
Attached patch (DERBY-733-more-exception-handling.diff) that addresses
Mike's concerns for exception handling. If something goes wrong when
locking, Derby will now fall back to the old behaviour.
Derbyall ran without failures.
% svn stat -q
M java/engine/org/apache/derby/impl/store/raw/data/RAFContainer.java
> Starvation in RAFContainer.readPage()
> -------------------------------------
>
> Key: DERBY-733
> URL: http://issues.apache.org/jira/browse/DERBY-733
> Project: Derby
> Type: Improvement
> Components: Performance, Store
> Versions: 10.1.2.1, 10.2.0.0, 10.1.3.0, 10.1.2.2
> Environment: Solaris x86 and Linux with Sun JVM 1.5.0. Derby embedded and
> client/server.
> Reporter: Knut Anders Hatlen
> Assignee: Knut Anders Hatlen
> Attachments: DERBY-733-more-exception-handling.diff, DERBY-733.diff,
> Insert.java, Select.java
>
> When Derby is completely disk bound, threads might be starved in
> RAFContainer.readPage(). This is a real problem when multiple clients
> are repeatedly accessing one or a small number of large tables. In
> cases like this, I have observed very high maximum response times
> (several minutes in the worst cases) on simple transactions. The
> average response time is not affected by this.
> The starvation is caused by a synchronized block in
> RAFContainer.readPage():
> synchronized (this) {
> fileData.seek(pageOffset);
> fileData.readFully(pageData, 0, pageSize);
> }
> If many threads want to read pages from the same file, there will be a
> long queue of threads waiting for this monitor. Since the Java
> specification does not guarantee that threads waiting for monitors are
> treated fairly, some threads might have to wait for a long time before
> they get the monitor. (Usually, a couple of threads get full throughput
> while the others have to wait.)
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