Hi there. I'm finally getting round to adding AUTO_INCREMENT support
to our storage engine.
As suggested at
http://forge.mysql.com/w/index.php?title=MySQL_Internals_Custom_Engine&printable=yes#Adding_Support_for_INSERT_to_a_Storage_Engine
I added the following code to my write_row method:
if (table->next_number_field && buf == table->record[0])
update_auto_increment();
But, when I then try to insert two rows without specifying the
auto_incrementing PK, the first row gets a PK of 1... and then I get a
PK collision error on the second one.
As far as I can see, the auto_increment isn't incrementing.
So I dug a bit in other storage engines: many of them support a
HA_STATUS_AUTO flag to the info method, and set
stats.auto_increment_value from somewhere in their internals. And in
the source code for update_auto_increment in handler.cc, is the
following interesting comment:
/*
Record this autogenerated value. If the caller then
succeeds to insert this value, it will call
record_first_successful_insert_id_in_cur_stmt()
which will set first_successful_insert_id_in_cur_stmt if it's not
already set.
*/
This seems to suggest the handler has to confirm it's used an
auto_increment value, so perhaps the reason I'm getting 1 every time
is because I'm not doing that.
But the only reference to first_successful_insert_id_in_cur_stmt I
find in the storage subtree is in ha_federated, which does this:
ha_federated::info(HA_STATUS_AUTO);
thd->first_successful_insert_id_in_cur_stmt=
stats.auto_increment_value;
Looking through the different storage engines, many of them seem to
"do things" relating to auto_increment when creating or opening
tables, but they all do different things.
So what's required to implement auto_increment?
I just want to get some auto_increment numbers, that obey
auto_increment_increment and auto_increment_offset as we are a multi-
master replication system - I might be interested in making up my own
numbers in future, but for now, I just want numbers! If I have to
implement my own counter and manage its state between restarts, I can,
but I get the impression MySQL is willing to handle that for me...
Thanks,
ABS
--
Alaric Snell-Pym ACGI MIAP MBCS
Chief software engineer, GenieDB
alaric@stripped
