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Revise documentation in QueueModel to clarify the meaning of 'outstanding' and 'penalty'

This commit is contained in:
Zhe Wu 2021-02-23 12:20:05 -08:00
parent 8ee7ee9e45
commit 25a7f87433
1 changed files with 14 additions and 12 deletions
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26
fdbrpc/QueueModel.h
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@ -27,21 +27,23 @@
#include "flow/Knobs.h" #include "flow/Knobs.h"
#include "flow/ActorCollection.h" #include "flow/ActorCollection.h"
/* // The data structure used for the client-side load balancing algorithm to
The data structure used for the client-side load balancer to decide which // decide which storage server to read data from. Conceptually, it tracks the
storage server to read data from. Conceptually, it represents the size of // number of outstanding requests the current client sent to each storage
storage server read request queue. One QueueData represents one storage // server. One "QueueData" represents one storage server.
server.
*/
struct QueueData { struct QueueData {
// The latest queue size in this storage server. // The current outstanding requests sent by the local client to this storage
// server. The number is smoothed out over a continuous timeline.
Smoother smoothOutstanding; Smoother smoothOutstanding;
// The last client perceived latency to this storage server.
double latency; double latency;
// The additional queue size used in the next request to this storage // Represents the "cost" of each storage request. By default, the penalty is
// server. This penalty is sent from the storage server from the last // 1 indicates that each outstanding request corresponds 1 outstanding
// request, which is the server side mechanism to ask the client to slow // request. However, storage server can also increase the penalty if it
// down request. // decides to ask the client to slow down sending requests to it. Penalty
// is updated after each LoadBalancedReply.
double penalty; double penalty;
// Do not consider this storage server if the current time hasn't reach this // Do not consider this storage server if the current time hasn't reach this
@ -69,7 +71,7 @@ public:
// Finishes the request sent to storage server with `id`. // Finishes the request sent to storage server with `id`.
// - latency: the measured client-side latency of the request. // - latency: the measured client-side latency of the request.
// - penalty: the server side penalty sent along with the response from // - penalty: the server side penalty sent along with the response from
// the storage server. // the storage server. Requires >= 1.
// - delta: Update server `id`'s queue model by substract this amount. // - delta: Update server `id`'s queue model by substract this amount.
// This value should be the value returned by `addRequest` below. // This value should be the value returned by `addRequest` below.
// - clean: indicates whether the there was an error or not. // - clean: indicates whether the there was an error or not.