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STCS_backlog: protect against negative backlog

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A negative backlog can be interpreted as a very large backlog.
Part of that is because we keep the total_size as an unsigned type,
which is what we expect. But in case there is an issue-- like an
exception that causes some SSTable not to be tracked then this size
can become negative. Returning a zero backlog is better than allowing
it to be interpreted as a giant number.

Signed-off-by: Glauber Costa <glauber@scylladb.com>
This commit is contained in:
Glauber Costa
2018-05-19 22:09:55 -04:00
parent 4b4e9f6c8c
commit 3e08bd17f0
1 changed files with 5 additions and 4 deletions
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9
sstables/size_tiered_backlog_tracker.hh
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@@ -76,11 +76,11 @@
// certain point in time, whose size is the amount of bytes currently written. So all we need
// to do is keep track of them too, and add the current estimate to the static part of (4).
class size_tiered_backlog_tracker final : public compaction_backlog_tracker::impl {
uint64_t _total_bytes = 0;
int64_t _total_bytes = 0;
double _sstables_backlog_contribution = 0.0f;
struct inflight_component {
uint64_t total_bytes = 0;
int64_t total_bytes = 0;
double contribution = 0;
};
@@ -115,11 +115,12 @@ public:
inflight_component compacted = compacted_backlog(oc);
auto total_bytes = _total_bytes + partial.total_bytes - compacted.total_bytes;
if ((total_bytes == 0)) {
if ((total_bytes <= 0)) {
return 0;
}
auto sstables_contribution = _sstables_backlog_contribution + partial.contribution - compacted.contribution;
return (total_bytes * log4(total_bytes)) - sstables_contribution;
auto b = (total_bytes * log4(total_bytes)) - sstables_contribution;
return b > 0 ? b : 0;
}
virtual void add_sstable(sstables::shared_sstable sst) override {