CodingClues - Latest Comments in Preventing Database Race Conditions

Re: Preventing Database Race Conditions

Tobias — Tue, 30 Sep 2008 05:51:57 -0000

yeah all this should be no big deal when you are using mysql 5 w/ transactions (which i'm not and was not refering to in this article)
thx

Re: Preventing Database Race Conditions

lino — Tue, 30 Sep 2008 05:34:51 -0000

When your racing inserts are not using the same DB connection then at least mysql_insert_id() will work, as that is just a wrapper to a C API call and said call is "client-connection-aware".
I am not sure about the SELECT LAST_INSERT_ID though, that might actually be a problem (if not client-connection-aware), although inside of a transaction it should work even with concurrent inserts from other threads.

Re: Preventing Database Race Conditions

Tobias — Tue, 30 Sep 2008 05:16:01 -0000

thanks, never heared of this LAST_INSERT_ID statement before
I had abstracted from the actual PHP code in this example (therefore no identifier)

Re: Preventing Database Race Conditions

Sebastian — Tue, 30 Sep 2008 05:14:51 -0000

I already pointed that out to Tobias.

However, the problem is, when you have e.g. 2 racing inserts, you only get the last ID of the two, but not the last two IDs. For Tobias' application, he needed exactly the one ID that he used in his INSERT, not the last one.

Re: Preventing Database Race Conditions

lino — Tue, 30 Sep 2008 04:38:17 -0000

While your solution might work, mysql_insert_id() or, if you are using a BIGINT as auto_increment mysql_query('SELECT LAST_INSERT_ID() FROM table') is the better solution. Don't forget to pass the resource_identifier of your mysql connection. And I ideally, if you are using MySQL 5, encapsulate the whole operation into a transaction.