Well… nearly any engine.<\/p>\n
I have a plan forming in my head to add some hooks to engines to help with creating temporary tables (the ones created while executing a query, not ones created during ALTER TABLE).<\/p>\n
Currently, if you ALTER TABLE and we require a temporary table, it’s still database.table but we generate a table name that’s small, unique and begins with “#sql”.<\/p>\n
I’ve changed some of the handler interface to accept two strings (database name, table name) instead of one “path” that may (or may not) end in “.FRM” and may (or may not) begin with “.\/” and may (or may not) use the “\/” separator between database and table name (hint: on win32, it’s sometimes “”).<\/p>\n
So ha_delete_table is now: ha_delete_table(db, table_name). Sanity!<\/p>\n
(this has the downside of being a incompatible change that doesn’t break the build as there seems to be no way in C++ to say “derived classes cannot implement a function of this name”).<\/p>\n
This is annoying for temporary tables however.<\/p>\n
They don’t reside in a database… they’re off in la-la land (otherwise known as opt_drizzle_tmpdir).<\/p>\n
Now… in MySQL 5.1 the ability for multiple temporary directories was added, and the MySQL server will cycle through them. The clusterfuck part of this was that a mutex was added… so every time the code goes to get the name of a (or for 99.99999999% of cases, the) temporary directory, it has to grab a mutex. With modern systems being able to have *many* simultaneous IO operations (e.g. create files) this is just dumb. It’s gone.<\/p>\n
If you want to use multiple spindles for temporary tables it’s called RAID people (or buy an SSD, mkfs.ext2 it and just wipe it on reboot. simple.)<\/p>\n
Anyway… back to temporary tables:<\/p>\n
they’re in \/tmp or something. So an API that’s foo(const char *db, const char *table_name) doesn’t work as well.<\/p>\n
Also, for a bunch of engines, it’s good to know that you’re using a temporary table. You probably want to store these somewhere that never needs fsync() or anything like that. If the server goes away, these tables are *gone*. So optimise for that.<\/p>\n
Heck, it may even be good to store temporary tables in your distributed engine (if that engine is memory based) as it’s often faster to access remote memory than local disk (although with SSD this is a whole different ball game… in fact, I’m not sure if it’s even still a ball game.. it’s possibly frisbee)<\/p>\n
But currently there’s hardcoded a mi_create (MyISAM create) call in the server and in the 6.0-maria tree, an #ifdef around if it’s mi_create or maria_create.<\/p>\n
So not any engine yet… but one can dream. Yes, I dare to dream.<\/p>\n
(although why I was dreaming of a small board with a PowerPC 603, 8MB RAM and a mini DVI port the other night is quite beyond me)<\/p>\n","protected":false},"excerpt":{"rendered":"
Well… nearly any engine. I have a plan forming in my head to add some hooks to engines to help with creating temporary tables (the ones created while executing a query, not ones created during ALTER TABLE). Currently, if you … Continue reading