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## Summary Event reads scoped to a set of channels pushed one bind parameter per channel: `channel_id IN ($5, $6, …)`. This applies to a viewer's access scope, which the relay adds to every REQ and `/query` without an `#h`, and to explicit multi-value `#h` filters. As a result, the SQL text depended on the viewer's channel count, and every count was a separate prepared statement. That caused two problems in production: - **Re-planning on every call.** A connection rarely reused a cached plan for these reads, so Postgres planned each one again. With no `since`, the plan covers every `events` partition. For `#p` mention reads (the `event_mentions` join), planning took far longer than executing the query. - **Hidden cost.** Monitoring that groups by statement split one query into one row per channel count, so its total cost never showed up in a single place. This PR binds the set as `channel_id = ANY($n)`, so one statement serves every channel count. On a production replica, the same query prepared with `ANY($5)` moved to Postgres's cached generic plan by its sixth run. Planning time dropped to near zero, and that plan was no slower than the custom one. ## What changed - `push_channel_scope` in `crates/buzz-db/src/store/event.rs` builds the channel-scope predicate as one array bind. - `build_query_events_sql` and `count_events_sql` each had their own copy of this block. Both now call the helper. - Semantics are unchanged: - Access scope still keeps channel-less global events. - Explicit `#h` still matches only the requested channels. - An empty set still means "no channels". ## What got simpler Two duplicated 20-line blocks became one helper. The statement count for channel-scoped reads no longer grows with channel count. ## Generic-plan exposure These statements were already persistent prepared statements, so a cached generic plan was always possible whenever the connection's statement cache held one. This change makes that reuse consistent; it doesn't introduce generic plans. Tag-value reads (`has_tag_values`) still run unnamed, as before. Plain (non-`#p`) access-scoped reads stay on custom plans. A production replica, with a viewer in hundreds of channels, ran the plain page read repeatedly under the default `plan_cache_mode`, and every run used the custom ordered index scan. Postgres estimated the generic plan as far more expensive, and when forced, it was orders of magnitude slower. Postgres switches only when the generic plan is no costlier than the average custom plan, so it never chose this one. The generic plan's cost comes from the `LIMIT` and `kind` values it can't see, not from the array length, and the per-arity `IN (…)` statements had the same blind spot. ## Tests - `channel_scope_sql_does_not_depend_on_channel_count` (unit): for the `#p` join and plain reads, for access scope and explicit `#h`, in both the page SELECT and the COUNT, the SQL for 1 channel equals the SQL for 40 channels. It also checks that the SQL uses `ANY(` and that global rows are retained only for access scope. - `channel_scoped_mention_reads_share_one_prepared_statement` (Postgres): on one connection, access-scoped `#p` reads with 1, 2 and 3 channels leave exactly one prepared `event_mentions` statement. With one mention per channel, one global mention, and one in an unscoped channel, every scope of 0–3 channels, with and without globals, returns and counts exactly its own rows. - The existing scope semantics tests still pass: - `access_scope_is_applied_before_historical_page_limit` - the explicit multi-channel `#h` page and count test - Mutation: reverting the helper to one bind per channel fails both new tests. ## Identified debt (not in this PR) - `get_last_message_at_bulk` still builds an `IN (…)` list per channel. It's a separate, lower-volume statement. - Superseded versions of replaceable roster events (kind 39002) keep their `event_mentions` rows. On large channels, a viewer's roster mention rows grow with every membership change. That's a follow-up. 🤖 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>