optimize(remove) usage of client's pending_querybuf (#10413)

To remove `pending_querybuf`, the key point is reusing `querybuf`, it means master client's `querybuf` is not only used to parse command, but also proxy to sub-replicas.

1. add a new variable `repl_applied` for master client to record how many data applied (propagated via `replicationFeedStreamFromMasterStream()`) but not trimmed in `querybuf`.

2. don't sdsrange `querybuf` in `commandProcessed()`, we trim it to `repl_applied` after the whole replication pipeline processed to avoid fragmented `sdsrange`. And here are some scenarios we cannot trim to `qb_pos`:
    * we don't receive complete command from master
    * master client blocked because of client pause
    * IO threads operate read, master client flagged with CLIENT_PENDING_COMMAND

    In these scenarios, `qb_pos` points to the part of the current command or the beginning of next command, and the current command is not applied yet, so the `repl_applied` is not equal to `qb_pos`.

Some other notes:
* Do not do big arg optimization on master client, since we can only sdsrange `querybuf` after data sent to replicas.
* Set `qb_pos` and `repl_applied` to 0 when `freeClient` in `replicationCacheMaster`.
* Rewrite `processPendingCommandsAndResetClient` to `processPendingCommandAndInputBuffer`, let `processInputBuffer` to be called successively after `processCommandAndResetClient`.

1 files changed, 2 insertions, 1 deletions

diff --git a/src/replication.c b/src/replication.c
index b93c512fc..e9a754ab4 100644
--- a/src/replication.c
+++ b/src/replication.c
@@ -3197,7 +3197,8 @@ void replicationCacheMaster(client *c) {
      * offsets, including pending transactions, already populated arguments,
      * pending outputs to the master. */
     sdsclear(server.master->querybuf);
-    sdsclear(server.master->pending_querybuf);
+    server.master->qb_pos = 0;
+    server.master->repl_applied = 0;
     server.master->read_reploff = server.master->reploff;
     if (c->flags & CLIENT_MULTI) discardTransaction(c);
     listEmpty(c->reply);