Hi,
I'm interested in this patch and I also run the same test with Ikeda-san's
fxact_update.pgbench.
In my environment (poor spec VM), the result is following.
* foreign_twophase_commit = disabled
363tps
* foreign_twophase_commit = required (It is necessary to set -R ${RATE} as
Ikeda-san said)
13tps
I analyzed the bottleneck using pstack and strace.
I noticed that the open() during "COMMIT PREPARED" command is very slow.
In my environment the latency of the "COMMIT PREPARED" is 16ms.
(On the other hand, the latency of "COMMIT" and "PREPARE TRANSACTION" is 1ms)
In the "COMMIT PREPARED" command, open() for wal segment file takes 14ms.
Therefore, open() is the bottleneck of "COMMIT PREPARED".
Furthermore, I noticed that the backend process almost always open the same wal
segment file.
In the current patch, the backend process on foreign server which is associated
with the connection from the resolver process always run "COMMIT PREPARED"
command.
Therefore, the wal segment file of the current "COMMIT PREPARED" command
probably be the same with the previous "COMMIT PREPARED" command.
In order to improve the performance of the resolver process, I think it is
useful to skip closing wal segment file during the "COMMIT PREPARED" and reuse
file descriptor.
Is it possible?
Regards,
Ryohei Takahashi
