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John
Asked: 2021-10-15 05:05:00 +0800 CST

AWS RDS MySQL connection limits

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I have a MySQL database server, db.t3.micro, parameter group is 'default.mysql8.0', max_connections is '{DBInstanceClassMemory/12582880}'

I figured out that it cannot handle more than ~63 connections

According to AWS RDS documentation https://docs.aws.amazon.com/AmazonRDS/latest/UserGuide/CHAP_Limits.html#RDS_Limits.MaxConnections

Connection limit for Mysql is calculated using '{DBInstanceClassMemory/12582880}' formula, where DBInstanceClassMemory tier instance memory in bytes.

So for db.t3.micro 1Gb it is 1073741824/12582880 = 85

‘SHOW VARIABLES LIKE "max_connections";’ returns 63

Tier Memory, GiB Memory, Bytes Calculated connection limit Real connection limit
db.t3.micro 1 1073741824 85 63
db.t3.small 2 2147483648 170 146
db.t3.2xlarge 32 32x1073741824 2720 2634

Why real connections limit is less than the formula result?

amazon-web-services amazon-rds

1 Answers

  1. Best Answer

    So DBInstanceClassMemory is actually TotalMemory- (Memory consumed by OS + other processes)

    Amazon documentation clearly says

    db.m5.xlarge instance class. DBInstanceClassMemory is 16 GiB, or 17,179,869,184 bytes

    but that is not true, and real DBInstanceClassMemory will be less than 16GiB

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