Details
Major Description
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.)