On 2013-09-13 13:12, Brian Craft wrote:
I'm testing different insert scenarios.
I was surprised to find that doing "insert into .. select * from .."
from a large table is an order of magnitude slower than running
individual "insert" commands for each row from a file. That is, if I
load file -> table A with insert commands, then do "insert into B
select * from A", the latter is 10x slower than the former.
That's very definitely off. Not sure what exactly, it's hard to say
without seeing the code.
Also, "create table B ... as select * from A" is impossibly fast. I'm
guessing this is not touching the disk unless it's in a transaction,
or something.
It definitely touches the disk, it just does a optimised data copy.
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