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Re: MySQL 8 - terrible performance
Posted by: Dimitri Kravtchuk
Date: April 30, 2019 02:21PM

Hi Hans,

I tried to reproduce your "mysqlslap" issue on 12cores Intel desktop.
Following the same steps as you do, here is what I have :

* MySQL 5.7 :

Benchmark
Average number of seconds to run all queries: 15.377 seconds
Minimum number of seconds to run all queries: 15.027 seconds
Maximum number of seconds to run all queries: 15.727 seconds
Number of clients running queries: 20
Average number of queries per client: 50

* MySQL 8.0 :

Benchmark
Average number of seconds to run all queries: 14.001 seconds
Minimum number of seconds to run all queries: 13.562 seconds
Maximum number of seconds to run all queries: 14.440 seconds
Number of clients running queries: 20
Average number of queries per client: 50

roughly 14sec for 8.0 and 15sec for 5.7

I used default config settings for both, except few options to make both versions at least compatible on used charset, collation, SSL, binlog :

[mysqld]
innodb_buffer_pool_size=2000M
ssl=0
default_authentication_plugin=mysql_native_password
skip_log_bin=1
character_set_server=latin1
collation_server=latin1_swedish_ci
skip-character-set-client-handshake

NOTE: your dataset is slightly bigger than default InnoDB Buffer Pool (BP) size, so I used 2G size to avoid unnecessary I/O (in case it's related to the storage difference).

Profiling processing of both MySQL versions is showing that main CPU cycles are spent for both in copying memory (and this is as expected, keeping in mind the nature of queries you're running), nothing "suspecting"..

Thus my question: is execution of 5 "full table scans" queries for 2000 times concurrently really representative for your production workload ?..

Rgds,
-Dimitri

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