Long-running processes in Serverless Environments

Last week I launched Gumcrm, and I wanted to share some issues I had with long-running functions on Vercel and Supabase.

Requirement - 25,128 DB calls under 1 min

My app syncs Gumroad sales and contacts. Since I'm using my SaaS boilerplate, every sale row needs a lot of Database queries:

1. Insert sale row
2. Check if the current subscription can add another contact
3. Check if the current user has entity.contacts.create
4. Grab the next contact folio (CTC-0001, CTC-0002...)
5. Insert/update contact row
6. Insert/update dynamic row values (custom properties)
7. Insert log
8. Call events.rows.created webhook event
9. Insert company if any (repeats 2-8 steps but for company)
10. Insert contact tags based on sale (churned, active....)
11. Insert entity.contacts.tags if didn't exist (for filtering/reporting...)

18 database calls for each sale. I have 1,396 gumroad "sales" (some are $0), that's 1,396 x 18 = 25,128 DB calls.

Problem #1 - Database (Supabase) timeout

On local development (M1 + postgres.app), it took 15 seconds to insert those 1k+ sales + contacts + companies.

On "launch day" (last Friday), I was ready to test in production (Supabase), but the first problem I encountered was:

Error: Timed out fetching a new connection from the pool. Please consider reducing the number of requests or increasing the `connection_limit` parameter (https://www.prisma.io/docs/concepts/components/prisma-client/connection-management#connection-pool). Current limit: 10.

I thought doing what the error message said would fix it:

• Set connection_limit to 0, 1, 2, 5, 10, 20...
• Set pool_timeout to 0, 1, 2, 5, 10, 20...

But this led to the next problem.

Problem #2 - Host (Vercel) timeout

It seemed like I "fixed" the problem... connection pool now waited for all incoming DB calls. But now I got a Vercel timeout error:

504 Error 'FUNCTION_INVOCATION_TIMEOUT'.

After a bit of research, I remembered that Vercel's Hobby plans allow for 10-second functions and Pro plans give 60-second functions, but my function lasted more than that, and +60s-functions is only for Enterprise customers.

I tried everything:

• Remove logs, webhook calls, company inserts...
• Use Prisma.createMany function (does not return created IDs)
• Go through each line of code to fix "N+1 select" problems
• Played more with connection_limit and pool_timeout

I was really worried that my boilerplate was not production-ready, but then I thought of something in the shower at 4 am.

Solution - Batches of 250 rows

It may seem obvious now, but the solution was simple:

Send batches of 250 rows (yes, I tried batches of 100, 200, 500, 1,000...).

This is how it looks now on development (15s) and production (55s).