Exercise 2: Measuring an Index — Possible Solution
====================================================

1. Seed a realistic volume (dev database only). createMany is far
   faster than 100,000 separate creates:

   const author = await prisma.user.create({ data: { email: "bulk@test.local" } });
   for (let batch = 0; batch < 100; batch++) {
     await prisma.post.createMany({
       data: Array.from({ length: 1000 }, (_, i) => {
         const n = batch * 1000 + i;
         return {
           title: `Post ${n}`,
           slug: `bulk-${n}`,
           authorId: author.id,
           published: n % 3 !== 0,
           createdAt: new Date(Date.now() - n * 60_000),
         };
       }),
     });
   }

2. Measure before adding the index:

   const plan = await prisma.$queryRaw`
     EXPLAIN ANALYZE
     SELECT "id", "title" FROM "Post"
     WHERE "published" = true ORDER BY "createdAt" DESC LIMIT 20
   `;

   Typical result:  Limit -> Sort -> Seq Scan on "Post"
                    (reads all 100,000 rows, then sorts them)

3. Add the index and migrate:

   @@index([published, createdAt(sort: Desc)])
   npx prisma migrate dev --name post-published-created-index

4. Measure again:

   Typical result:  Limit -> Index Scan using "Post_published_createdAt_idx"
                    (reads just the first 20 matching entries)

What changed: before, PostgreSQL had to read every row and sort the
matches itself; with the index, published posts are already stored in
createdAt order, so it can read the first 20 entries and stop. The
"actual time" figure typically drops by a large factor. Exact numbers
and index names depend on your data and PostgreSQL version.

WHY THIS WORKS AS AN ANSWER
------------------------------
It follows the chapter's rule — measure, change one thing, measure
again — with enough data for the difference to be real (on a table of
a few dozen rows PostgreSQL may reasonably ignore the index). The
index columns match the query exactly: an equality filter first
(published), then the sort column in the same direction (createdAt
DESC).