Details
Major Description
For writing the transaction log to disk Derby uses a
RandomAccessFile. If it is supported by the JVM, the log files are
opened in "rws" mode making the file system take care of syncing
writes to disk. "rws" mode will ensure that both the data and the file
meta-data is updated for every write to the file. On some operating
systems (e.g. Solaris) this leads to two write operation to the disk
for every write issued by Derby. This is limiting the throughput of
update intensive applications. If we could change the file mode to
"rwd" this could reduce the number of updates to the disk.
I have run some simple tests where I have changed mode from "rws" to
"rwd" for the Derby log file. When running a small numbers of
concurrent client threads the throughput is almost doubled and the
response time is almost halved. I will attach some graphs that show
this when running a given number of concurrent "tpc-b" like clients. These
graphs show the throughput when running with "rws" and "rwd" mode when the
disk's write cache has been enabled and disabled.
I am creating this Jira to have a place where we can collect
information about issues both for and against changing the default
mode for writing to log files.
