[WIP] tests/integration/replication

tests/integration/replication.tcl

@@ -1551,7 +1551,9 @@ foreach disklessload {disabled on-empty-db} {
                 $replica config set repl-diskless-load $disklessload
 
                 # Populate replica with many keys, master with a few keys.
-                $replica debug populate 4000000
+                # Using 500K keys instead of 4M to reduce test time while still
+                # creating a sufficient LOADING window for high-frequency polling.
+                $replica debug populate 500000
                 populate 3 master 10
 
                 # Start the replication process...
@@ -1571,14 +1573,12 @@ foreach disklessload {disabled on-empty-db} {
                 # Discarding old db will take a long time and loading new one
                 # will be quick. So, if we receive -LOADING, most probably it is
                 # when flushing the db.
-                wait_for_condition 1 10000 {
+                # The LOADING window can be very brief (milliseconds on fast hardware),
+                # so we use high-frequency polling to reliably catch it.
+                wait_for_condition 1000 10 {
                     [catch {$replica ping} err] &&
                     [string match *LOADING* $err]
                 } else {
-                    # There is a chance that we may not catch LOADING response
-                    # if flushing db happens too fast compared to test execution
-                    # Then, we may consider increasing key count or introducing
-                    # artificial delay to db flush.
                     fail "Replica did not reply LOADING."
                 }