## Summary
Whereas currently we send all WAL to all pageserver shards, and each
shard filters out the data that it needs,
in this RFC we add a mechanism to filter the WAL on the safekeeper, so
that each shard receives
only the data it needs.
This will place some extra CPU load on the safekeepers, in exchange for
reducing the network bandwidth
for ingesting WAL back to scaling as O(1) with shard count, rather than
O(N_shards).
Touches #9329.
## Checklist before requesting a review
- [ ] I have performed a self-review of my code.
- [ ] If it is a core feature, I have added thorough tests.
- [ ] Do we need to implement analytics? if so did you add the relevant
metrics to the dashboard?
- [ ] If this PR requires public announcement, mark it with
/release-notes label and add several sentences in this section.
## Checklist before merging
- [ ] Do not forget to reformat commit message to not include the above
checklist
---------
Co-authored-by: Vlad Lazar <vlalazar.vlad@gmail.com>
Co-authored-by: Vlad Lazar <vlad@neon.tech>
