# Description of Changes
We've run into a problem on Maincloud caused by a database that was
writing a relatively small number of very large transactions. This was
accruing many commitlog segments consuming hundreds of gigabytes of
disk, but had not ever taken a snapshot, or compressed or archived any
data, as the database had not progressed past one million transactions.
With this PR, we take a snapshot every time the commitlog segment
rotates. We still also snapshot every million transactions.
One BitCraft database we looked at had 2.5 million transactions per
commitlog segment, meaning that this change will not meaningfully affect
the frequency of snapshots. The offending Maincloud database, however,
had only 50 transactions per segment!
# API and ABI breaking changes
N/a
# Expected complexity level and risk
3: Hastily made changes to finnicky code across several crates.
# Testing
I am unsure how to test these changes.
- [ ] <!-- maybe a test you want to do -->
- [ ] <!-- maybe a test you want a reviewer to do, so they can check it
off when they're satisfied. -->
Defines the canonical commitlog payload, and how to encode / decode it.
Also exposes folds alongside iterators, which allows the common case of
replaying the commitlog onto a database to be further optimized (the
`Txdata` does not have to be constructed in this case). This
optimization is, however, left for a future patch.
Phoebe Goldman