Hello, I posted our fix at lp:~prohaska7/maria/5.5-savepoint-offset-fix. Does it make sense? Thanks Rich Prohaska
On Mon, Jul 9, 2012 at 7:17 PM, Rich Prohaska <[email protected]> wrote: > Hello, > It turns out the previous explanation was WRONG. > > Here is another stab at the problem. My understanding of the savepoint > initialization process is: > 1. the handlerton sets its savepoint_offset to the size of its local > savepoint data. > 2. the ha_initailize_handlerton function reads it, modifies its idea of the > total savepoint data size, and sets it to the offset of the handlerton's > local state > > If this is correct, then why does the ha_initialize_handlerton function do > step (2) twice? It looks like a code merge bug to me. > > Rich Prohaska > > On Mon, Jul 9, 2012 at 4:41 PM, Rich Prohaska <[email protected]> wrote: >> >> Hello, >> >> We observed a problem with savepoints in Mariadb 5.5.25. The problem at >> the SQL layer is that a "rollback to savepoint" statement would get an error >> after the savepoint was created. The problem was caused by the savepoint >> name in the savepoint stack getting overwritten by the handlerton >> savepoint_set method. >> >> Here is what we think is going on: >> 1. space is reserved in the savepoint memory for each handlerton in the >> ha_initialize_handlerton function. >> 2. then space is reserved for the SAVEPOINT object in ha_init. (Yes, >> ha_init gets called AFTER the ha_initialize_handlerton calls. >> 3. ha_savepoint computes the address of the handlerton's object as >> (uchar*)(sv+1) + ht->savepoint_offset. this assumes that the SAVEPOINT >> object is laid out first, followed by the handlerton's space. >> unfortunately, step (1) occurs before step (2) so this is not the case. >> >> Here is a possible fix: >> Move the base initialization of the savepoint_alloc_size from ha_init to >> the global intiializer. With this change, the handlerton's offsets are >> computed AFTER the SAVEPOINT space is reserved. >> >> Is this correct? >> >> Thanks >> Rich Prohaska >> > _______________________________________________ Mailing list: https://launchpad.net/~maria-developers Post to : [email protected] Unsubscribe : https://launchpad.net/~maria-developers More help : https://help.launchpad.net/ListHelp
