On Jul 2, 2010, at 1:08 PM, Suchit Kaura wrote:
We are seriously considering removing the
layoutcommit call from the file layout client.
From the RFC5661:
For block/volume-based layouts, LAYOUTCOMMIT may require updating the
block list that comprises the file and committing this layout to
stable storage. For file-based layouts, synchronization of
attributes between the metadata and storage devices, primarily the
size attribute, is required.
The control protocol is free to synchronize the attributes before it
receives a LAYOUTCOMMIT; however, upon successful completion of a
LAYOUTCOMMIT, state that exists on the metadata server that
describes
the file MUST be synchronized with the state that exists on the
storage devices that comprise that file as of the client's last sent
operation. Thus, a client that queries the size of a file between a
WRITE to a storage device and the LAYOUTCOMMIT might observe a size
that does not reflect the actual data written.
I understand and agree with the option that control protocol will
update the
information on the MDFS for file layout type but does the text above
not mark
layout commit as a consistency boundary even with servers supporting
filelayouts?
For the file layout type, the COMMIT operation does this already, and
the LAYOUTCOMMIT is not needed. My reading of the above text is that
if a LAYOUTCOMMIT is sent and successfully completed then the 'MUST be
synchronized with the state ..... " text applies. But why would the
file layout type want two synchronization points (LAYOUTCOMMIT and
COMMIT)? So, why send a LAYOUTCOMMIT for the file layout type?
or are we saying that every write or DFS must be synchronized with
MDFS thru control protocol for file layout servers?
Nope, only on COMMIT.
-->Andy
Regards,
Suchit
Andy Adamson <andros@...> writes:
On Jul 1, 2010, at 8:07 PM, Sandeep Joshi wrote:
Hi Sandeep
In certain cases, I don't see layoutcommit on a file at all even
after doing many writes.
FYI:
You should not be paying attention to layoutcommits - they have no
value for the file layout type.
From RFC 5661:
"The LAYOUTCOMMIT operation commits chages in the layout represented
by the current filehandle, client ID (derived from the session ID in
the preceding SEQUENCE operation), byte-range, and stateid."
For the block layout type, this sentence has meaning in that there is
a layoutupdate4 payload that enumerates the blocks that have changed
state from being 'handed out' to being 'written'.
The file layout type has no layoutupdate4 payload, and the layout
does
not change due to writes, and thus the LAYOUTCOMMIT call is useless.
The only field in the LAYOUTCOMMIT4args that might possibly be useful
is the loca_last_write_offset which tells the server what the client
thinks is the EOF of the file after WRITE. It is an extremely lame
server (file layout type server) that depends upon clients for this
info.
Client side operations:
open
write(s)
close
On server side (observed operations):
open
layoutget's
close
But, I do not see laycommit at all. In terms data written by client
it is about 4-5MB.
When does client issue laycommit?
The latest linux client sends a layout commit when the VFS does a
super_operations.write_inode call which happens when the metadata of
an inode needs updating. We are seriously considering removing the
layoutcommit call from the file layout client.
-->Andy
regards,
Sandeep
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