## Problem
Postgres will often immediately follow a relation existence check with a
relation size query. This incurs two roundtrips, and may prevent
effective caching.
See [Slack
thread](https://databricks.slack.com/archives/C091SDX74SC/p1751951732136139).
Touches #11728.
## Summary of changes
For the gRPC API:
* Add an `allow_missing` parameter to `GetRelSize`, which returns
`missing=true` instead of a `NotFound` error.
* Remove `CheckRelExists`.
There are no changes to libpq behavior.
## Problem
With gRPC `GetPageRequest` batches, we'll have non-trivial
fragmentation/reassembly logic in several places of the stack
(concurrent reads, shard splits, LFC hits, etc). If we included the
block numbers with the pages in `GetPageResponse` we could have better
verification and observability that the final responses are correct.
Touches #11735.
Requires #12480.
## Summary of changes
Add a `Page` struct with`block_number` for `GetPageResponse`, along with
the `RelTag` for completeness, and verify them in the rich gRPC client.
## Problem
`GetPageRequest::request_id` is supposed to be a unique ID for a
request. It's not, because we may retry the request using the same ID.
This causes assertion failures and confusion.
Touches #11735.
Requires #12480.
## Summary of changes
Extend the request ID with a retry attempt, and handle it in the gRPC
client and server.
## Problem
The gRPC API does not provide LSN leases.
## Summary of changes
* Add LSN lease support to the gRPC API.
* Use gRPC LSN leases for static computes with `grpc://` connstrings.
* Move `PageserverProtocol` into the `compute_api::spec` module and
reuse it.
## Problem
gRPC base backups use gRPC compression. However, this has two problems:
* Base backup caching will cache compressed base backups (making gRPC
compression pointless).
* Tonic does not support varying the compression level, and zstd default
level is 10% slower than gzip fastest level.
Touches https://github.com/neondatabase/neon/issues/11728.
Touches https://github.com/neondatabase/cloud/issues/29353.
## Summary of changes
This patch adds a gRPC parameter `BaseBackupRequest::compression`
specifying the compression algorithm. It also moves compression into
`send_basebackup_tarball` to reduce code duplication.
A follow-up PR will integrate the base backup cache with gRPC.
## Problem
Full basebackups are used in tests, and may be useful for debugging as
well, so we should support them in the gRPC API.
Touches #11728.
## Summary of changes
Add `GetBaseBackupRequest::full` to generate full base backups.
The libpq implementation also allows specifying `prev_lsn` for full
backups, i.e. the end LSN of the previous WAL record. This is omitted in
the gRPC API, since it's not used by any tests, and presumably of
limited value since it's autodetected. We can add it later if we find
that we need it.
## Problem
The gRPC base backup implementation has a few issues: chunks are not
properly bounded, and it's not possible to omit the LSN.
Touches #11728.
## Summary of changes
* Properly bound chunks by using a limited writer.
* Use an `Option<Lsn>` rather than a `ReadLsn` (the latter requires an
LSN).
## Problem
The page API gRPC errors need a few tweaks to integrate better with the
GetPage machinery.
Touches https://github.com/neondatabase/neon/issues/11728.
## Summary of changes
* Add `GetPageStatus::InternalError` for internal server errors.
* Rename `GetPageStatus::Invalid` to `InvalidRequest` for clarity.
* Rename `status` and `GetPageStatus` to `status_code` and
`GetPageStatusCode`.
* Add an `Into<tonic::Status>` implementation for `ProtocolError`.
## Problem
A binary Protobuf schema descriptor can be used to expose an API
reflection service, which in turn allows convenient usage of e.g.
`grpcurl` against the gRPC server.
Touches #11728.
## Summary of changes
* Generate a binary schema descriptor as
`pageserver_page_api::proto::FILE_DESCRIPTOR_SET`.
* Opportunistically rename the Protobuf package from `page_service` to
`page_api`.
## Problem
For the [communicator
project](https://github.com/neondatabase/company_projects/issues/352),
we want to move to gRPC for the page service protocol.
Touches #11728.
## Summary of changes
This patch adds an experimental gRPC Protobuf schema for the page
service. It is equivalent to the current page service, but with several
improvements, e.g.:
* Connection multiplexing.
* Reduced head-of-line blocking.
* Client-side batching.
* Explicit tenant shard routing.
* GetPage request classification (normal vs. prefetch).
* Explicit rate limiting ("slow down" response status).
The API is exposed as a new `pageserver/page_api` package. This is
separate from the `pageserver_api` package to reduce the dependency
footprint for the communicator. The longer-term plan is to also split
out e.g. the WAL ingestion service to a separate gRPC package, e.g.
`pageserver/wal_api`.
Subsequent PRs will: add Rust domain types for the Protobuf types,
expose a gRPC server, and implement the page service.
Preliminary prototype benchmarks of this gRPC API is within 10% of
baseline libpq performance. We'll do further benchmarking and
optimization as the implementation lands in `main` and is deployed to
staging.
