How to reference DBInstanceVCPU in RDS parameter?


Per the docs here, DBInstanceVCPU should be supported.

However, I've noted that in the default.aurora-postgresql13 this seems to be formatted differently (note the $ vs lack thereof):

max_connections : LEAST({DBInstanceClassMemory/9531392},5000)
max_parallel_workers : GREATEST(${DBInstanceVCPU/2},8)

Moreover, if I try to create a custom parameter group and edit max_parallel_workers by simply changing the 8 to another integer, the UI refuses to accept anything with DBInstanceVCPU (with or without the $).

Is this an issue with the RDS UI's parameter validation or is there something else that I'm missing?


1 Answer
Accepted Answer


Please note, I confirm this is a known issue and currently the "DBInstanceVCPU" cannot be used/re-used in parameter value when being modified from customer's end. This makes "DBInstanceVCPU" unusable for customer. Apologies, that AWS public documentation [1] is misleading and I will report it to our internal team.

max_parallel_workers={DBInstanceVCPU/4*3} ----> is not accepted as a valid entry
max_parallel_workers=GREATEST({DBInstanceVCPU*3/4},1) ----> is accepted as a valid entry


[1] Working with DB parameter groups - DB parameter formulas -

Hope it helps and if it does, I would appreciate if answer can be accepted so that community can benefit for clarity when searching for similar enquiries in repost/aws guide.

Thank you!

answered 2 months ago
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reviewed 2 months ago

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