Why do too many requests overwhelm the server?

is there a boss who can elaborate on the process of the explosion? Such as instruction calls, memory. Thank you

Jun.10,2022

it is generally said that too many requests will overwhelm the server, which means "denial of service", right? The server doesn't have to hang up.

the number of concurrent connections per service is limited, and each request arrives-> processes-> responses take time and resources.

it's easy to understand that there are too many concurrent requests:
1) when the number of concurrent connections to the service is full (unable to handle it, so there are no free connections available), new requests will not be processed normally.
2) when processing a request, contention for resources (such as CPU and disk IO) and taking up more capacity than the server causes processing time to be too long, and then causes the connection to be full.

MySQL Query : SELECT * FROM `codeshelper`.`v9_news` WHERE status=99 AND catid='6' ORDER BY rand() LIMIT 5
MySQL Error : Disk full (/tmp/#sql-temptable-64f5-1b305bf-2bcee.MAI); waiting for someone to free some space... (errno: 28 "No space left on device")
MySQL Errno : 1021
Message : Disk full (/tmp/#sql-temptable-64f5-1b305bf-2bcee.MAI); waiting for someone to free some space... (errno: 28 "No space left on device")
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