From 131da3085695bb13797254a32c8ccc8da21d545f Mon Sep 17 00:00:00 2001
From: Calle Wilund <calle@scylladb.com>
Date: Mon, 31 May 2021 16:18:27 +0000
Subject: [PATCH] table: Always use explicit commitlog discard + clear out
 rp_set

Fixes #8733

If a memtable flush is still pending when we call table::clear(),
we can end up doing a "discard-all" call to commitlog, followed
by a per-segment-count (using rp_set) _later_. This will foobar
our internal usage counts and quite probably cause assertion
failures.
Fixed by always doing per-memtable explicit discard call. But to
ensure this works, since a memtable being flushed remains on
memtable list for a while (why?), we must also ensure we clear
out the rp_set on discard.

Closes #8766
---
 memtable.hh | 4 ++--
 table.cc    | 4 +++-
 2 files changed, 5 insertions(+), 3 deletions(-)

diff --git a/memtable.hh b/memtable.hh
index 3a78c734f7..5752880408 100644
--- a/memtable.hh
+++ b/memtable.hh
@@ -272,8 +272,8 @@ public:
     const db::replay_position& replay_position() const {
         return _replay_position;
     }
-    const db::rp_set& rp_set() const {
-        return _rp_set;
+    db::rp_set rp_set() {
+        return std::exchange(_rp_set, {});
     }
     friend class iterator_reader;
 
diff --git a/table.cc b/table.cc
index b801c4a9ea..7a9ae7f41f 100644
--- a/table.cc
+++ b/table.cc
@@ -1504,7 +1504,9 @@ bool table::can_flush() const {
 future<> table::clear() {
     _memtables->clear_and_add();
     if (_commitlog) {
-        _commitlog->discard_completed_segments(_schema->id());
+        for (auto& t : *_memtables) {
+            _commitlog->discard_completed_segments(_schema->id(), t->rp_set());
+        }
     }
     return _cache.invalidate(row_cache::external_updater([] { /* There is no underlying mutation source */ }));
 }