Remote File Access (RFA) allows for data compression. RFA
data compression can provide faster data transfer, especially over
a slow link and when the file being remotely accessed has large
records with repeated characters.To invoke data compression for
the RFA service, specify the keyword, COMP,
in the DSLINE command. The COMP
keyword compresses both NFT and RFA data associated to the remote
environment specified in the DSLINE command.
For example, issuing the command DSLINE NODE1;COMP
allows for compression of all RFA and NFT data to the remote node
called NODE1.
To terminate data compression to the specified environment,
specify the keyword NOCOMP in the
on of any new remote files opened as well as prevents data compression
of any future NFT data to the environment specified in the DSLINE
command. Files opened remotely while compression is in effect for
the environment remain in compressed mode even after the DSLINE;NOCOMP
command is issued.
The same algorithm is used for both RFA and NFT data compression.
The same algorithm is also used with DS Services compression: each
sequence of up to 64 consecutive repeated characters is compressed
to two bytes, and repeated blanks are compressed to one byte.
Without RFA compression enabled, the RFA service can transfer
up to 29,900 bytes of data at one time. However, due to overhead
associated with managing a compressed data transfer, the RFA service
with compression enabled can transfer up to a maximum of 29,000
bytes of data at one time between MPE/iX-based HP 3000s. For transfers
between an MPE/iX-based system and an MPE-V based system the maximum
amount of compressed data that can be transferred at one time is
14,500 bytes.
RFA compression only compresses data transmitted with the
FREAD, FREADDIR,
FREADBACKWARD, FWRITE,
FWRITEDIR and FUDPATE
intrinsics. Therefore, RFA compression is not supported with the
Remote DataBase Access (RDBA) service.
RFA compression is currently only available on HP 3000 Series
900 systems with version B.00.05 or later of the NS 3000/iX
Network Services. If you request RFA compression of a file residing
on a system that does not support RFA compression (such as systems
running NS 3000/V software released prior to version A.00.12),
RFA completes the request without compressing the RFA data. No error
or warning messages are issued in this situation.
