How to handle issues when we run out of connections to database? -


i looking commonly used / best practices in industry.

assume following hypothetical scenario: if app server accepts 200 user requests, , each of them need db access. db max_connections 100.

if 200 users request @ same time, have 100 max_connections, happens other requests, not served max connections ?

in real world:

  1. will remaining 100 requests stored in sort of queue on apps servers, , kept waiting db connections ?

  2. do error out ?

basically, if database server can handle 100 connections, , of web connections "require database access," must ensure no more 100 requests allowed active @ 1 instant.   “ruling constraint” of scenario.   (it may 1 of many.)

you can accept "up 200 simultaneous connections" on server, must enqueue these requests limit of 100 active requests not exceeded.

there many, many ways that:   load balancers, application servers, apache/nginix directives. sometimes, web-page front-end process broken-out among many different servers working in parallel. no matter how it, there must way regulate how many requests active, , queue remainder.

also note that, though might have “200 active connections” web server, highly unlikely 200 of these clients “clicked mouse @ precisely same time.”   requests come in @ random rates , therefore might never encounter sort of delay @ all. system must nonetheless engineered handle worst case.


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