Re: Questions about buffered streams
Roedy Green wrote:
Did you read my essay at http://mindprod.com/jgloss/buffer.html
If you did, please read it again and tell me where you got
confused.
failure_to@yahoo.co.uk wrote:
I'm not sure how you got the impression that article got me
confused?
Perhaps it was your assertion that 64K individual writes of one byte would
proceed faster than a single write of 64K bytes that gave that impression.
So in theory, above code would write those 64000 bytes to a
system in aprox the same amount of time as Buffered stream
would, assuming no other thread blocks this output stream?
No.
64K one-byte writes will be *much* slower than one 64 KB write.
Are you talking about the code below or about buffered streams? I know
from your article that using buffers can cause some overhead due to
bytes being copied to buffer, but from my understanding fo object
doesn't buffer these bytes, but sends them directly to the system ... so
in theory ( well mine, much flawed theory )the below code should write
those bytes to the system faster than buffered stream would ( assuming
the disk isn't constantly spinning :) ... which apparently it is )
No.
Even assuming you're writing to a disk, your Java write operation is so far
removed from "spinning" that it isn't even remotely useful to think of it in
those terms.
You have Java flushing to a system buffer, which writes to a driver, which
loads data onto a disk-controller cache if there is one, which loads data onto
the disk's own cache, which loads data onto the disk platter(s). Assuming no
RAID, which adds some overhead of multiple-disk synchronization. OSes have
'fsync' and such modes that determine if writes go all the way to platter
before reporting completion, which may or may not be engaged.
Anyway, each individual write has to go through all those layers - 64000 times
for one byte apiece will always lose to 64KB through the gate in a single rush.
--
Lew