perf: reduce pg_notify call volume by batching together agent metadata updates (#21330)

---------

Signed-off-by: Callum Styan <callumstyan@gmail.com>
Co-authored-by: Claude Sonnet 4.5 <noreply@anthropic.com>

coderd/database/queries.sql.go

@@ -17954,6 +17954,47 @@ func (q *sqlQuerier) UpdateVolumeResourceMonitor(ctx context.Context, arg Update
 	return err
 }
 
+const batchUpdateWorkspaceAgentMetadata = `-- name: BatchUpdateWorkspaceAgentMetadata :exec
+WITH metadata AS (
+	SELECT
+		unnest($1::uuid[]) AS workspace_agent_id,
+		unnest($2::text[]) AS key,
+		unnest($3::text[]) AS value,
+		unnest($4::text[]) AS error,
+		unnest($5::timestamptz[]) AS collected_at
+)
+UPDATE
+	workspace_agent_metadata wam
+SET
+	value = m.value,
+	error = m.error,
+	collected_at = m.collected_at
+FROM
+	metadata m
+WHERE
+	wam.workspace_agent_id = m.workspace_agent_id
+	AND wam.key = m.key
+`
+
+type BatchUpdateWorkspaceAgentMetadataParams struct {
+	WorkspaceAgentID []uuid.UUID `db:"workspace_agent_id" json:"workspace_agent_id"`
+	Key              []string    `db:"key" json:"key"`
+	Value            []string    `db:"value" json:"value"`
+	Error            []string    `db:"error" json:"error"`
+	CollectedAt      []time.Time `db:"collected_at" json:"collected_at"`
+}
+
+func (q *sqlQuerier) BatchUpdateWorkspaceAgentMetadata(ctx context.Context, arg BatchUpdateWorkspaceAgentMetadataParams) error {
+	_, err := q.db.ExecContext(ctx, batchUpdateWorkspaceAgentMetadata,
+		pq.Array(arg.WorkspaceAgentID),
+		pq.Array(arg.Key),
+		pq.Array(arg.Value),
+		pq.Array(arg.Error),
+		pq.Array(arg.CollectedAt),
+	)
+	return err
+}
+
 const deleteOldWorkspaceAgentLogs = `-- name: DeleteOldWorkspaceAgentLogs :execrows
 WITH
 	latest_builds AS (