chore: convert tailnet tables to UNLOGGED for improved write performance (#21607)

This migration converts all tailnet coordination tables to UNLOGGED:
- `tailnet_coordinators`
- `tailnet_peers`
- `tailnet_tunnels`

UNLOGGED tables skip Write-Ahead Log (WAL) writes, significantly
improving performance for high-frequency updates like coordinator
heartbeats and peer state changes.

The trade-off is that UNLOGGED tables are truncated on crash recovery
and are not replicated to standby servers. This is acceptable for these
tables because the data is ephemeral:
1. Coordinators re-register on startup
2. Peers re-establish connections on reconnect
3. Tunnels are re-created based on current peer state

**Migration notes:**
- Child tables must be converted before the parent table because LOGGED
child tables cannot reference UNLOGGED parent tables (but the reverse is
allowed)
- The down migration reverses the order: parent first, then children

Fixes https://github.com/coder/coder/issues/21333

coderd/database/dump.sql

@@ -1762,14 +1762,14 @@ CREATE TABLE site_configs (
     value text NOT NULL
 );
 
-CREATE TABLE tailnet_coordinators (
+CREATE UNLOGGED TABLE tailnet_coordinators (
     id uuid NOT NULL,
     heartbeat_at timestamp with time zone NOT NULL
 );
 
 COMMENT ON TABLE tailnet_coordinators IS 'We keep this separate from replicas in case we need to break the coordinator out into its own service';
 
-CREATE TABLE tailnet_peers (
+CREATE UNLOGGED TABLE tailnet_peers (
     id uuid NOT NULL,
     coordinator_id uuid NOT NULL,
     updated_at timestamp with time zone NOT NULL,
@@ -1777,7 +1777,7 @@ CREATE TABLE tailnet_peers (
     status tailnet_status DEFAULT 'ok'::tailnet_status NOT NULL
 );
 
-CREATE TABLE tailnet_tunnels (
+CREATE UNLOGGED TABLE tailnet_tunnels (
     coordinator_id uuid NOT NULL,
     src_id uuid NOT NULL,
     dst_id uuid NOT NULL,

coderd/database/migrations/000411_tailnet_tables_unlogged.down.sql

@@ -0,0 +1,10 @@
+-- Revert tailnet tables to LOGGED (standard WAL-enabled tables).
+-- WARNING: This requires a full table rewrite with WAL generation,
+-- which can be slow for large tables.
+
+-- Convert parent table first (before children, reverse of up migration).
+ALTER TABLE tailnet_coordinators SET LOGGED;
+
+-- Convert child tables after parent.
+ALTER TABLE tailnet_peers SET LOGGED;
+ALTER TABLE tailnet_tunnels SET LOGGED;

coderd/database/migrations/000411_tailnet_tables_unlogged.up.sql

@@ -0,0 +1,20 @@
+-- Convert all tailnet coordination tables to UNLOGGED for improved write performance.
+-- These tables contain ephemeral coordination data that can be safely reconstructed
+-- after a crash. UNLOGGED tables skip WAL writes, significantly improving performance
+-- for high-frequency updates like coordinator heartbeats and peer state changes.
+--
+-- IMPORTANT: UNLOGGED tables are truncated on crash recovery and are not replicated
+-- to standby servers. This is acceptable because:
+-- 1. Coordinators re-register on startup
+-- 2. Peers re-establish connections on reconnect
+-- 3. Tunnels are re-created based on current peer state
+
+-- Convert child tables first (they have FK references to tailnet_coordinators).
+-- UNLOGGED child tables can reference LOGGED parent tables, but LOGGED child
+-- tables cannot reference UNLOGGED parent tables. So we must convert children
+-- before converting the parent.
+ALTER TABLE tailnet_tunnels SET UNLOGGED;
+ALTER TABLE tailnet_peers SET UNLOGGED;
+
+-- Convert parent table last (after all children are unlogged).
+ALTER TABLE tailnet_coordinators SET UNLOGGED;