Forum: Managing VoltDB

Post: Snapshot causes all sp stopped

Snapshot causes all sp stopped
tony7889
Aug 1, 2011
Hi,

I am now trying to build a VoltDB with Python Client, I created several processes to do the massive insert, But I found that, the performance is quite weird, the performance drops, and sp executed drops to 0 for a few seconds, and the performance raises again. and it is very periodical.

After spending some time, I found the the snapshot cause the performance drop which the performance drop is gone when I turn off the snapshot.

It is weird, in paper, the snapshot is async process, but now I found the snapshot can affact the performance, so this is a config issue or a bug?

Thanks,
Tony Li
Hi Tony, In the current
aweisberg
Aug 1, 2011
Hi Tony,

In the current version of VoltDB online snapshots are very bursty. When the snapshot starts the system blocks while serializing 256 megabytes of snapshot data before allow the snapshot save procedure to return. This causes throughput to drop to 0 when you start a snapshot. If a data set is small enough you will never see throughput recover before the snapshot completes. Given enough time the system will recover but will still experience some pauses. Improvements that do a better job of scheduling snapshot work out over time are on trunk and will be released at the end of the current iteration.

Ariel