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, 1 insertions, 6 deletions

diff --git a/src/blocked.c b/src/blocked.c
index 2754da9e0..65b584213 100644
--- a/src/blocked.c
+++ b/src/blocked.c
@@ -141,12 +141,7 @@ void processUnblockedClients(void) {
          * the code is conceptually more correct this way. */
         if (!(c->flags & CLIENT_BLOCKED)) {
             /* If we have a queued command, execute it now. */
-            if (processPendingCommandsAndResetClient(c) == C_OK) {
-                /* Now process client if it has more data in it's buffer. */
-                if (c->querybuf && sdslen(c->querybuf) > 0) {
-                    if (processInputBuffer(c) == C_ERR) c = NULL;
-                }
-            } else {
+            if (processPendingCommandAndInputBuffer(c) == C_ERR) {
                 c = NULL;
             }
         }