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Request #77116 implement in_transaction handler for pdo_mysql
Submitted: 2018-11-07 11:51 UTC Modified: 2020-09-23 09:53 UTC
From: remy dot fox at hotmail dot com Assigned: nikic (profile)
Status: Closed Package: PDO MySQL
PHP Version: irrelevant OS:
Private report: No CVE-ID: None
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 [2018-11-07 11:51 UTC] remy dot fox at hotmail dot com 
Description:
------------
PDO has a function called 'inTransaction', which verifies whether a transaction is currently active. As far as I can see it calls a method 'in_transaction' here: https://github.com/php/php-src/blob/master/ext/pdo/pdo_dbh.c (line 656). 

When I start the transaction using SQL ("START TRANSACTION") instead of the PDO API, the result of inTransaction is always false. However, I'm confident a transaction is running, because calling "ROLLBACK" does not commit any changes. On MariaDB, the following query results "1", too: SELECT SESSION_VALUE FROM INFORMATION_SCHEMA.SYSTEM_VARIABLES WHERE VARIABLE_NAME = 'in_transaction'.

So I suspect that there is something wrong with the inTransaction method. It only seems to work when it is called in combination with beginTransaction, rather than in any case that a transaction was started.

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 [2018-11-08 16:22 UTC] adambaratz@php.net
-Type: Bug +Type: Feature/Change Request
 [2018-11-08 16:22 UTC] adambaratz@php.net 
What you're experiencing is maybe not the best behavior, but pdo_mysql performing as it's written. This driver doesn't define an in_transaction method, so it defaults to checking the status of the bit flipped by the beginTransaction/rollBack/commit methods.

An in_transaction method could be implemented in ext/pdo_mysql/mysql_driver.c (see the definition of mysql_methods at the bottom of that file for where the connection is made). If there's a C API for checking transaction status, that would likely be more reliable than running a query. See the pgsql_handle_in_transaction function in ext/pdo_pgsql/pgsql_driver.c for an example of this. FWIW, pdo_pgsql is the only PDO driver shipped with PHP that implements this function.
 [2018-11-08 16:23 UTC] adambaratz@php.net
-Summary: PDO inTransaction does not have the same value as SESSION_VARIABLE +Summary: implement in_transaction handler for pdo_mysql
 [2018-11-08 16:23 UTC] adambaratz@php.net
-Operating System: Windows +Operating System: -PHP Version: 7.2.11 +PHP Version: irrelevant
 [2018-11-08 17:21 UTC] requinix@php.net 
The Python API gets its in_transaction from MYSQL->server_status & 1.
 [2018-11-12 12:42 UTC] remyfox at hotmail dot com 
In MySQL table schema structure changes such as CREATE TABLE cause an automatic commit of the transaction. PDO.inTransaction always reacted to this, so I suspect that it does not only check a bit flipped by beginTransaction/rollBack/commit methods.
 [2018-11-12 13:09 UTC] remyfox at hotmail dot com 
I see that my memory was not correct. Apparently, the implicit commit after a table schema modification is not noticed by the current PDO.inTransaction implementation.

Regardless, I would say this is a bug rather than a feature request.
 [2020-09-23 09:53 UTC] nikic@php.net
-Status: Open +Status: Closed -Assigned To: +Assigned To: nikic
 [2020-09-23 09:53 UTC] nikic@php.net 
Has been implemented by https://github.com/php/php-src/pull/4996.
 
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