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reader_concurrency_semaphore: add trace points for important events

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Notably, to admission execution and eviction. Registering/unregistering
the permit as inactive is not traced, as this happens on every
buffer-fill for range scans.
Semaphore trace messages have a "[reader_concurrency_semaphore]" prefix
to allow them to be clearly associated with the semaphore.
This commit is contained in:
Botond Dénes
2023-03-20 10:40:15 -04:00
parent 1f51f752cc
commit ff87f95a26
1 changed files with 22 additions and 0 deletions
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22
reader_concurrency_semaphore.cc
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@@ -50,6 +50,15 @@ struct reader_concurrency_semaphore::inactive_read {
}
};
template <>
struct fmt::formatter<reader_concurrency_semaphore::evict_reason> : fmt::formatter<std::string_view> {
template <typename FormatContext>
auto format(const reader_concurrency_semaphore::evict_reason& reason, FormatContext& ctx) const {
static const char* value_table[] = {"permit", "time", "manual"};
return fmt::format_to(ctx.out(), "{}", value_table[static_cast<int>(reason)]);
}
};
namespace {
void maybe_dump_reader_permit_diagnostics(const reader_concurrency_semaphore& semaphore, std::string_view problem) noexcept;
@@ -878,6 +887,8 @@ future<> reader_concurrency_semaphore::execution_loop() noexcept {
permit.on_executing();
auto e = std::move(permit.aux_data());
tracing::trace(permit.trace_state(), "[reader concurrency semaphore] executing read");
try {
e.func(reader_permit(permit.shared_from_this())).forward_to(std::move(e.pr));
} catch (...) {
@@ -1105,6 +1116,7 @@ void reader_concurrency_semaphore::do_detach_inactive_reader(reader_permit::impl
ir.ttl_timer.cancel();
ir.detach();
ir.reader.permit()->on_evicted();
tracing::trace(permit.trace_state(), "[reader_concurrency_semaphore] evicted, reason: {}", reason);
try {
if (ir.notify_handler) {
ir.notify_handler(reason);
@@ -1261,8 +1273,17 @@ future<> reader_concurrency_semaphore::do_wait_admission(reader_permit::impl& pe
&stats::reads_queued_because_count_resources
};
static const char* result_as_string[] = {
"admitted immediately",
"queued because of non-empty ready list",
"queued because of used permits",
"queued because of memory resources",
"queued because of count resources"
};
const auto [admit, why] = can_admit_read(permit);
++(_stats.*stats_table[static_cast<int>(why)]);
tracing::trace(permit.trace_state(), "[reader concurrency semaphore] {}", result_as_string[static_cast<int>(why)]);
if (admit != can_admit::yes || !_wait_list.empty()) {
auto fut = enqueue_waiter(permit, wait_on::admission);
if (admit == can_admit::yes && !_wait_list.empty()) {
@@ -1273,6 +1294,7 @@ future<> reader_concurrency_semaphore::do_wait_admission(reader_permit::impl& pe
maybe_dump_reader_permit_diagnostics(*this, "semaphore could admit new reads yet there are waiters");
maybe_admit_waiters();
} else if (admit == can_admit::maybe) {
tracing::trace(permit.trace_state(), "[reader concurrency semaphore] evicting inactive reads in the background to free up resources");
++_stats.reads_queued_with_eviction;
evict_readers_in_background();
}