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Bug #81155 Mysql close is NOT synchronous
Submitted: 2021-06-17 14:35 UTC Modified: 2023-01-14 16:45 UTC
Avg. Score:3.0 ± 0.0
Reproduced:0 of 0 (0.0%)
From: video dot ice dot power at seznam dot cz Assigned:
Status: Open Package: PDO MySQL
PHP Version: 8.0.7 OS: any
Private report: No CVE-ID: None
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From: video dot ice dot power at seznam dot cz
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 [2021-06-17 14:35 UTC] video dot ice dot power at seznam dot cz
Mysql close is NOT synchronous - it does NOT wait until the connection is closed/released by the database server which causes more simultaneous connections than needed from a script than connect/disconnect from the same database often.

An example of such usecase is unit testing.

I have tested also PostgreSQL. This PDO driver handles close synchronously/ok (SQL to limit connections: ALTER ROLE user CONNECTION LIMIT 1).

MySQL driver needs to be fixed as even server limit of 2 is not enough, currently limit of like 5 is needed even if there is no more than 1 simultaneous client connection.

Test script:
# 1. limit connection limit to 1
php -r '(new PDO("mysql:host=mysql", "user", "pass"))->exec("ALTER USER '"'"'user'"'"'@'"'"'%'"'"' WITH MAX_USER_CONNECTIONS 1");'

# 2. connect/disconnect often
for ($i = 0; $i < 10000; $i++) {
    (new PDO("mysql:host=mysql", "user", "pass"))->exec("SELECT 1");

Expected result:
no error

Actual result:
connection limit is exhausted about every 1000th connection


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 [2023-01-14 16:45 UTC]
This could also be a problem with MySQL server. FWIW I cannot reproduce it on my machine.
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