We could give some numbers for connection pool size / concurrency limits for Serverless AWS Lambda or link to GitHub issue

To me my default thinking was that Lambda only have 1 CPU, looking on Google says that sometimes they have 2 but real testing below says it’s always 2 so it could be nice to have a reference to that in the docs section for users:

Memory (MB)	CPU (Cores)	Default Pool Size (= 2 * CPU + 1)
128	2	5
256	2	5
512	2	5
1024	2	5
2048	2	5
3008	2	5

So now I just changed the memory setting, but the reported cpu value is always the same, meaning we’ll give 2 IO threads per lambda and 5 connections.

And to be clear. This is what we see from the OS layer. It might be wrong, it might be less or more. But the system sees 2 and will act based on that.

_Originally posted by @pimeys in https://github.com/prisma/prisma/issues/942#issuecomment-558153490_

Different popular PostgreSQL instances and their limits:

Instance Size	used_at_start	max_conn	res_for_super	res_for_normal
t2.micro	7	87	3	77
t2.small	7	198	3	188
t2.medium	7	413	3	403
t2.large	7	856	3	846
t2.xlarge	7	1743	3	1733
t2.2xlarge	7	3518	3	3508
m5.large	7	823	3	813
m5.xlarge	7	1691	3	1681
m5.2xlarge	7	3429	3	3419
m5.4xlarge	7	5000	3	4990

Some of the connections are used already when the instance is running, so I’d base my calculations for the connections reserved for normal users (the last column).

So with the default pool size of five connections: Lambda Concurrency Limit based on Different popular PostgreSQL instances

Instance Size	Lambda Concurrency Limit
t2.micro	15
t2.small	37
t2.medium	80
t2.large	169
t2.xlarge	346
t2.2xlarge	701
m5.large	162
m5.xlarge	336
m5.2xlarge	683
m5.4xlarge	998

_Originally posted by @pimeys in https://github.com/prisma/prisma/issues/942#issuecomment-558269427_

[mhwelander]

Added link to this in doc.

[mhwelander]

@Jolg42 Salutations - could you tell me a bit more about when a user might want this information? Is it something I would mention in the deployment docs?

Does it change this sentence?

Serverless (FaaS): It’s recommended to set the connection limit to 1 if you’re not using an external connection pooler because each incoming request starts a short-

And what does “Lambda Concurrency Limit based on Different popular PostgreSQL instances” affect?