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repair/row_level: remove reader timeout

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This timeout was added to catch reader related deadlocks. We have not
seen such deadlocks for a long time, but we did see false-timeouts
caused by this, see explanation below. Since the cost now outweight the
benefit, remove the timeout altogether.

The false timeout happens during mixed-shard repair. The
`reader_permit::set_timeout()` call is called on the top-level permit
which repair has a handle on. In the case of the mixed-shard repair,
this belongs to the multishard reader. Calling set_timeout() on the
multishard reader has no effect on the actual shard readers, except in
one case: when the shard reader is created, it inherits the multishard
reader's current timeout. As the shard reader can be alive for a long
time, this timeout is not refreshed and ultimately causes a timeout and
fails the repair.

Refs: #18269

Closes scylladb/scylladb#20703
This commit is contained in:
Botond Dénes
2024-09-19 07:13:17 -04:00
committed by Kamil Braun
parent e67016540c
commit 3ebb124eb2
1 changed files with 0 additions and 6 deletions
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6
repair/row_level.cc
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@@ -349,11 +349,6 @@ repair_reader::repair_reader(
future<mutation_fragment_opt>
repair_reader::read_mutation_fragment() {
++_reads_issued;
// Use a very long timeout for the reader to break out any eventual
// deadlock within the reader. Thirty minutes should be more than
// enough to read a single mutation fragment.
auto timeout = db::timeout_clock::now() + std::chrono::minutes(30);
_reader.set_timeout(timeout); // reset to db::no_timeout in pause()
return _reader().then_wrapped([this] (future<mutation_fragment_opt> f) {
try {
auto mfopt = f.get();
@@ -397,7 +392,6 @@ void repair_reader::check_current_dk() {
}
void repair_reader::pause() {
_reader.set_timeout(db::no_timeout);
if (_reader_handle) {
_reader_handle->pause();
}