On 12/08/2015 02:53 AM, Shyam wrote:
That is the intent. The question is how do we specify the fops that we want to do and the arguments to the fop. In this approach, for example xl_fxattrop_writev() is a new FOP. List of fops that need to be done are fxattrop, writev in that order and the arguments are a union of the arguments needed to perform the fops fxattrop, writev. The reason why this fop is not implemented through out the graph is to not change most of the stack on the brick side in the first cut of the implementation. i.e. quota/barrier/geo-rep/io-threads priorities/bit-rot may have to implement these new compund fops. We still get the benefit of avoiding the network round trips.Hi,Why not think along the lines of new FOPs like fop_compound(_cbk) where, the inargs to this FOP is a list of FOPs to execute (either in order or any order)?
With a scheme like the above we could,- compound any set of FOPs (of course, we need to take care here, but still the feasibility exists)
It still exists but the fop space will be blown for each of the combination.
- Each xlator can inspect the compound relation and chose to uncompound them. So if an xlator cannot perform FOPA+B as a single compound FOP, it can choose to send FOPA and then FOPB and chain up the responses back to the compound request sent to it. Also, the intention here would be to leverage existing FOP code in any xlator, to appropriately modify the inargs - The RPC payload is constructed based on existing FOP RPC definitions, but compounded based on the compound FOP RPC definitionThis will be done in phase-3 after learning a bit more about how best to implement it to prevent stuffing arguments in xdata in future as much as possible. After which we can choose to retire compound-fop-sender and receiver xlators.
This will be done in phase-2. At the moment we are not giving any choice for the xlators on the brick side.Possibly on the brick graph as well, pass these down as compounded FOPs, till someone decides to break it open and do it in phases (ultimately POSIX xlator).
Yes. There was a discussion with krutika where if shard wants to do write then xattrop in a single fop, then we need dht to implement dht_writev_fxattrop which should look somewhat similar to dht_writev(), and afr will need to implement afr_writev_fxattrop() as full blown transaction where it needs to take data+metadata domain locks then do data+metadata pre-op then wind to compound_fop_sender_writev_fxattrop() and then data+metadata post-op then unlocks.The intention would be to break a compound FOP in case an xlator in between cannot support it or, even expand a compound FOP request, say the fxattropAndWrite is an AFR compounding decision, but a compound request to AFR maybe WriteandClose, hence AFR needs to extend this compound request.
If we were to do writev, fxattrop separately, fops will be (In unoptimized case):
1) finodelk for write 2) fxattrop for preop of write. 3) write 4) fxattrop for post op of write 5) unlock for write 6) finodelk for fxattrop 7) fxattrop for preop of shard-fxattrop 8) shard-fxattrop 9) fxattrop for post op of shard fxattrop 10) unlock forfxattropIf AFR chooses to implement writev_fxattrop: means data+metadata transaction. 1) finodelk in data, metadata domain simultaneously (just like we take multiple locks in rename)
2) preop for data, metadata parts as part of the compound fop 3) writev+fxattrop 4)postop for data, metadata parts as part of the compound fop 5) unlocks simultaneously.So it is still 2x reduction of the number of network fops except for may be locking.
We need to arrive at a consensus about how to specify the list of fops and their arguments. The reason why I went against list_of_fops is to make discovery of possibile optimizations we can do easier per compound fop (Inspired by ec's implementation of multiplications by all possible elements in the Galois field, where multiplication with different number has a different optimization). Could you elaborate more about the idea you have about list_of_fops and its arguments? May be we can come up with combinations of fops where we can employ this technique of just list_of_fops and wind. I think rest of the solutions you mentioned is where it will converge towards over time. Intention is to avoid network round trips without waiting for the whole stack to change as much as possible.The above is just a off the cuff thought on the same.
Pranith
The scheme below seems too specific to my eyes, and looks like we would be defining specific compound FOPs than the ability to have generic ones.On 12/07/2015 04:08 AM, Pranith Kumar Karampuri wrote:hi, Draft of the design doc: Main motivation for the design of this feature is to reduce network round trips by sending more than one fop in a network operation, preferably without introducing new rpcs. There are new 2 new xlators compound-fop-sender, compound-fop-receiver. compound-fop-sender is going to be loaded on top of each client-xlator on the mount/client and compound-fop-receiver is going to be loaded below server-xlator on the bricks. On the mount/client side from the caller xlator till compund-fop-encoder xlator, the xlators can choose to implement this extracompound fop handling. Once it reaches "compound-fop-sender" it will try tochoose a base fop on which it encodes the other fop in the base-fop's xdata,and winds the base fop to client xlator(). client xlator sends the base fop with encoded xdata to server xlator on the brick using rpc of the base fop. Once server xlator does resolve_and_resume() it will wind the base fop tocompound-fop-receiver xlator. This fop will decode the extra fop from xdata of the base-fop. Based on the order encoded in the xdata it executes separate fops one after the other and stores the cbk response arguments of both the operations. It again encodes the response of the extra fop on to the base fop's response xdata and unwind the fop to server xlator. Sends the response using base-rpc's response structure. Client xlator will unwind the base fop tocompound-fop-sender, which will decode the response to the compound fop'sresponse arguments of the compound fop and unwind to the parent xlators. I will take an example of fxattrop+write operation that we want to implement in afr as an example to explain how things may look. compound_fop_sender_fxattrop_write(call_frame_t *frame, xlator_t *this, fd_t * fd, gf_xattrop_flags_t flags, dict_t * fxattrop_dict, dict_t * fxattrop_xdata, struct iovec * vector, int32_t count, off_t off, uint32_t flags, struct iobref * iobref, dict_t * writev_xdata) ) { 0) Remember the compound-fop take base-fop as write() in wriev_xdata add the following key,value pairs 1) "xattrop-flags", flags 2) for-each-fxattrop_dict key -> "fxattrop-dict-<actual-key>", value 3) for-each-fxattrop_xdata key -> "fxattrop-xdata-<actual-key>", value 4) "order" -> "fxattrop, writev" 5) "compound-fops" -> "fxattrop" 6) Wind writev() } compound_fop_sender_fxattrop_write_cbk(...) { /*decode the response args and call parent_fxattrop_write_cbk*/ } <compound_fop_sender_parent>_fxattrop_write_cbk (call_frame_t *frame, void *cookie, xlator_t *this, int32_t fxattrop_op_ret, int32_t fxattrop_op_errno, dict_t *fxattrop_dict, dict_t *fxattrop_xdata, int32_t writev_op_ret, int32_t writev_op_errno, struct iatt *writev_prebuf, struct iatt *writev_postbuf, dict_t *writev_xdata) { /**/ } compound_fop_receiver_writev(call_frame_t *frame, xlator_t *this, fd_t * fd, struct iovec * vector, int32_t count, off_t off, uint32_t flags, struct iobref * iobref, dict_t * writev_xdata) {0) Check if writev_xdata has "compound-fop" else default_writev()2) decode writev_xdata from above encoding -> flags, fxattrop_dict, fxattrop-xdata 3) get "order" 4) Store all the above in 'local' 5) wind fxattrop() with compound_receiver_fxattrop_cbk_writev_wind() as cbk } compound_receiver_fxattrop_cbk_writev_wind (call_frame_t *frame, void *cookie, xlator_t *this, int32_t op_ret, int32_t op_errno, dict_t *dict, dict_t *xdata) { 0) store fxattrop cbk_args 1) Perform writev() with writev_params with compound_receiver_writev_cbk() as the 'cbk' } compound_writev_cbk (call_frame_t *frame, void *cookie, xlator_t *this, int32_t op_ret, int32_t op_errno, struct iatt *prebuf, struct iatt *postbuf, dict_t *xdata) { 0) store writev cbk_args 1) Encode fxattrop response to writev_xdata with similar encoding in the compound_fop_sender_fxattrop_write() 2) unwind writev() } This example is just to show how things may look, but the actual implementation may just have all base-fops calling common function to perform the operations in the order given in the receriver xl. Yet to think about that. It is probably better to Encode fop-number from glusterfs_fop_t rather than the fop-string in the dictionary. This is phase-1 of the change because we don't want to change RPCs in phase-2 we can implement the compound fops that are commonly used by lot of translators throughout the stack so that quota/bitrot/geo-rep/barrier etc handle them in phase-3 may be just in time for 4.0 we can convert them to on the wire RPCs Thanks to Raghavendra G, krutika, Ravi, Anuradha for the discussions Pranith _______________________________________________ Gluster-devel mailing list Gluster-devel@xxxxxxxxxxx http://www.gluster.org/mailman/listinfo/gluster-devel
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