is your app single threaded, if so group commit is not the issue.
What is your OS? What is your JVM? Derby may use different syncing
algorithms depending on JVM version.
How did you measure synchronous write, ie. did you
write a java program and execute against the same JVM as derby is
running in?
The disk that that contains the log directory is the one of interest.
Each transaction is made up of a number of log records. From your
description each transaction will have the following:
begin log record
insert log record for row into base table
insert log record for row into primary key index
commit log record
yarono wrote:
Hello,
I'm working on a simple db. Each record is composed of 3 long values. The
first two are the primary key.
I have to measure the performance of the insertions. Each insertion is
wrapped in a transaction, which is commited having only one insertion in it.
I've measured both berkeley db performance and postgres and got about
110-115 insertions per second.
Now in derby db (both in embeded mode and server mode) I get better
performance: about 250-300 insertions per second. This obviously results
from some kind of a group commit, although I get these results both when
auto-commiting or manual-commiting after each insertion.
I've performed a simple test of synchronious writing 24 bytes (3 * 8 bytes)
to the disk. It measure 117 writes per second, and I believe this is the
upper bound of any db performance.
So, I don't understand why I get such good performance, although I commit
after each insertion.
I examined the .dat files in both /log and /seg0 folders. None of them
increase in 24 bytes segments, but rathar bigger segments.
So, my questions are:
1. Which log file in /log or /seg0 should I examine to analyze the numebr of
bytes written each write to disk?
2. How do I disable the group commit or whatever attribute that causes this
communal write? how do I make each transaction be written on its own to the
disk?
Thanks in advance,
Yaron
