Optimize top_authors materialized view for better performance

- Limit materialized view to authors with followers_count > 0 and top 10k records
- Add proper indexes (search GIN, pubkey B-tree, followers_count DESC)
- Use CONCURRENTLY for non-blocking refreshes in cron job
- Reduces sorting overhead and memory usage during refresh

The original materialized view was expensive because it sorted all authors
regardless of follower count. This optimization reduces the dataset to a
manageable size while maintaining search functionality.

Fixes expensive query issue in top_authors materialized view.

packages/db/migrations/055_optimize_top_authors_view.ts

@@ -0,0 +1,43 @@
+import { type Kysely, sql } from 'kysely';
+
+// deno-lint-ignore no-explicit-any
+export async function up(db: Kysely<any>): Promise<void> {
+  // Drop the existing materialized view and its indexes
+  await sql`DROP MATERIALIZED VIEW IF EXISTS top_authors`.execute(db);
+
+  // Create a more optimized materialized view that limits the number of authors
+  // This reduces the sorting cost and memory usage during refresh
+  await sql`
+    CREATE MATERIALIZED VIEW top_authors AS
+    SELECT pubkey, followers_count, search
+    FROM author_stats
+    WHERE followers_count > 0  -- Only include authors with followers
+    ORDER BY followers_count DESC
+    LIMIT 10000  -- Limit to top 10k authors for search functionality
+  `.execute(db);
+
+  // Create indexes on the materialized view for better query performance
+  await sql`CREATE INDEX CONCURRENTLY IF NOT EXISTS top_authors_search_idx ON top_authors USING GIN (search gin_trgm_ops)`
+    .execute(db);
+  await sql`CREATE INDEX CONCURRENTLY IF NOT EXISTS top_authors_pubkey_idx ON top_authors (pubkey)`.execute(db);
+  await sql`CREATE INDEX CONCURRENTLY IF NOT EXISTS top_authors_followers_count_idx ON top_authors (followers_count DESC)`
+    .execute(db);
+
+  // Ensure the materialized view is populated with data immediately
+  await sql`REFRESH MATERIALIZED VIEW CONCURRENTLY top_authors`.execute(db);
+}
+
+export async function down(db: Kysely<unknown>): Promise<void> {
+  // Drop the optimized view and recreate the original one
+  await sql`DROP MATERIALIZED VIEW IF EXISTS top_authors`.execute(db);
+
+  await sql`
+    CREATE MATERIALIZED VIEW top_authors AS
+    SELECT pubkey, followers_count, search 
+    FROM author_stats 
+    ORDER BY followers_count DESC
+  `.execute(db);
+
+  await sql`CREATE INDEX top_authors_search_idx ON top_authors USING GIN (search gin_trgm_ops)`.execute(db);
+  await sql`CREATE INDEX top_authors_pubkey_idx ON top_authors (pubkey)`.execute(db);
+}

packages/ditto/cron.ts

@@ -19,6 +19,6 @@ export function cron(ctx: TrendsCtx) {
 
   Deno.cron('refresh top authors', '20 * * * *', async () => {
     const { kysely } = ctx.db;
-    await sql`refresh materialized view top_authors`.execute(kysely);
+    await sql`refresh materialized view CONCURRENTLY top_authors`.execute(kysely);
   });
 }