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gpfsDataShipStart_t Structure
flag before initiating data shipping, one of the participating nodes is chosen as the agent to which all
appends are shipped. The aggregate performance of all the appending nodes is limited to the
throughput of a single node in this case, but should still exceed what the performance would have been
for appending small records without using data shipping.
Data shipping mode imposes several restrictions on file usage:
v Because an application level read or write may be split across several agents, POSIX read and write
file atomicity is not enforced while in data shipping mode.
v A file in data shipping mode cannot be written through any file handle that was not associated with the
data shipping collective through a GPFS_DATA_SHIP_START directive.
v Calls that are not allowed on a file that has data shipping enabled:
– chmod
– fchmod
– chown
– fchown
– link
The GPFS_DATA_SHIP_START directive exits cleanly only when cancelled by a
GPFS_DATA_SHIP_STOP directive. If all threads issue a close for the file, it is taken out of data shipping
mode but errors are also returned.
Members
structLen Length of the gpfsDataShipStart_t structure.
structType Structure identifier GPFS_DATA_SHIP_START
numInstances The number of open file instances, on all nodes, collaborating to operate
on the file.
reserved This field is currently not used.
For compatibility with future versions of GPFS, set this field to zero.
Recovery
Since GPFS_DATA_SHIP_START directives block their invoking threads until all participants respond
accordingly, there needs to be a way to recover if the application program uses the wrong value for
numInstances or one of the participating nodes crashes before issuing its GPFS_DATA_SHIP_START
directive. While a gpfs_fcntl() subroutine is blocked waiting for other threads, the subroutine can be
interrupted by any signal. If a signal is delivered to any of the waiting subroutines, all waiting subroutine on
every node are interrupted and return EINTR. GPFS does not establish data shipping if such a signal
occurs.
It is the responsibility of the application to mask off any signals that might normally occur while waiting for
another node in the data shipping collective. Several libraries use SIGALRM; the thread that makes the
gpfs_fcntl() invocation should use sigthreadmask to mask off delivery of this signal while inside the
subroutine.
Error status
EINTR A signal was delivered to a blocked gpfs_fcntl() subroutine. All waiting subroutines, on
every node, are interrupted.
EINVAL The file mode has been changed since the file was opened to include or exclude
O_APPEND.
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