dCap is the native random access I/O protocol for files within
dCache. In additition to the usual data transfer mechanisms,
it supports all necessary file metadata and name space
manipulation operations.
In order to optimize I/O transferrates and memory consumption
dCap allows to configure parameters within the client and the
server. e.g:
TCP Socket send and receive buffer sizes.
I/O buffers sizes.
There are two parameters per I/O direction, determining the
actual TCP send/recv buffer size used for each transfer. Those
values can be set within the
config/pool.batch file on the pool nodes.
defaultSend/RecvBufferSize: this value is used if the dCap client doesn’t try to set this value. The default value for this parameter is 256K Bytes.maxSend/RecvBufferSize: this value is the maximum value, the mover is allowed to use. It’s used if either thedefaultSend/RecvBufferSizeis larger or the client asks for a larger value. The default value for this parameter is 1MBytes.
On the server side, the max/defaultSend/RecvBuffer value can
either be set in the config/pool.batch
file or in the config/*.poollist files.
Using the batch context :
set context dCap3-maxSendBufferSizevalue in bytesset context dCap3-maxRecvBufferSizevalue in bytesset context dCap3-defaultSendBufferSizevalue in bytesset context dCap3-defaultRecvBufferSizevalue in bytes
Or it may specified in the create ... command line
create diskCacheV111.pools.MultiProtocolPool2 ${0} \
"!MoverMap \
${1} \
-defaultSendBufferSize=value in bytes \
*** \
-${2} -${3} -${4} -${5} -${6} -${7} -${8} \
"
The most appropriate way to specify those values on the server
side is certainly to add the corresponding entry in the
config/...poollist. The entry would look
like
dcache30_1 /dcache/pool sticky=allowed maxSendBufferSize=value in bytes tag.hostname=dcache30 ***Please note the different ways of using the ’=’ and the ’-’ sign in the different alternatives.
For a full list of dCap library API calls and dccp options,
please refer to to
http://www.dcache.org/manuals/libdcap.shtml
and
http://www.dcache.org/manuals/dccp.shtml
respectively. To set the local and remote TCP buffer send and
receive buffers either use the API call
dc_setTCPSend/ReceiveBuffer(int size) or
the -r SIZE -s SIZE dccp options. In both
cases the value is transferred to the remote mover which tries
to set the corresponding values. Please not the the server
protects itself by having a maximum size for those values
which it doesn’t exceed. Please check the section ’TCP
send/recv buffer sizes from the servers point of view’ to
learn how to change those values.