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## What The relay's 1-second read caches (restriction state, tenant host, open channels) now date each entry from when the read checked out its pool connection, not from when the cache miss began. Concurrent misses on the restriction and tenant-host caches now share one database read. The open-channels cache already did this. ## Why Each of these caches serves an entry for 1 s after "the read that produced it began". Today that start time is taken before waiting for a pool connection. Once pool waits reach about a second (for example, many clients reconnecting at once), every entry is already expired by the time it lands. The cache hit rate falls toward zero exactly when the pool is saturated, so every request does its own read. Those reads queue for the same connections, which stretches the waits further. Requests that time out in the pool then fail closed (`internal error checking restriction state`, `community active check failed; refusing the socket`), and their clients reconnect and add more load. In a local synthetic reconnect load test with a 50-connection pool: - the restriction cache served fewer than one request in five from cache; - the tenant-host cache, which has a single key for the whole deployment, missed more often than it hit; - the open-channels cache missed hundreds of thousands of times on expired entries. ## How - **Stamp at checkout.** `buzz_db::ReadAt<T>` carries a value plus the instant its connection was checked out. The statement's snapshot is no older than that instant, so serving the value for 1 s after it keeps the documented staleness bound, however long the read queued. Three `*_read_at` methods return it: `moderation_restriction_state_read_at`, `lookup_community_by_host_read_at` and `get_listed_open_channel_ids_read_at`. The existing methods now call these and drop the value's timestamp. Each operation keeps one datastore span under its existing name, carried by the `*_read_at` method. - **Share concurrent misses.** `SharedReads<K>` is the per-key gate the open-channels cache already used, moved into its own module. The open-channels cache, the restriction cache and the tenant-host cache now all use it. The first miss reads; the others wait for it, then recheck the cache. A waiter waits for at most the writer pool's acquire timeout plus `SHARED_READ_STATEMENT_WAIT` (1 s). That covers the leader's own wait for a connection, which is what grows in a storm, so waiters keep sharing its read instead of queueing duplicate reads behind it. A failed or cancelled leader releases its waiters at once. A leader whose statement hangs stalls them for at most 1 s past the acquire timeout, never the statement timeout. - **Reject hosts no community can have.** `bind_community` rejects a host longer than `communities.host VARCHAR(255)` can hold (`buzz_core::tenant::MAX_HOST_LEN`, counted in characters) as unmapped, next to the empty-host check. An unauthenticated caller's arbitrarily long host therefore never reaches a resolver, cache, gate or the database. No staleness bound changes: every entry is still served for at most 1 s after its read's snapshot. Invalidation paths are unchanged. A read in flight at an invalidation can still refill the old row for at most that bound, as documented today. ## What got simpler The open-channels gate's hand-rolled `try_lock`/`timeout` block is replaced by `SharedReads::turn`. One gate implementation now serves three caches instead of one implementation that only one cache had. The gate's wait is set once per gate rather than passed at each call site. Provisioning and host binding share one `MAX_HOST_LEN` instead of a private constant. ## Tests - `shared_reads::tests`: one caller reads while the rest wait; a waiter gives up on a hung read after its bound. - `concurrent_restriction_and_host_misses_share_the_in_flight_read`: waiters on both caches use the leader's entry; with an unreachable database, any waiter that read on its own would fail. - `postgres_tests::cache_misses_behind_a_held_pool_share_one_fresh_read`: with a one-connection pool held for longer than every max age, eight concurrent misses on each of the three caches cost one database read, and each entry still lands fresh. - `tenant::tests::an_overlong_host_fails_closed_before_the_resolver`: a host over the limit fails as unmapped with no gate entry and no lookup; a host at the limit, including one in multibyte characters, is still looked up. - Mutation-checked: each of the following turns these tests red: stamping any of the three entries before the pool wait, dropping either new waiter path, letting waiters give up after the cache's max age, dropping the host length check, or counting the host length in bytes. 🤖 Generated with [Claude Code](https://claude.com/claude-code) --------- Signed-off-by: Luke Tornquist <tornquist@squareup.com> Co-authored-by: Elrond <28d6302a099e5225b02c4155ac4236e4912603df2ab08dbfc2f4fef08ce598c8@buzz.block.builderlab.xyz> Co-authored-by: Claude Opus 5.5 <noreply@anthropic.com>