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feat(server): Allow sampling arena stats from a specified thread (#428)

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Also update dense_set.md with a reproducable test on how to see memory differences
of DenseSet vs RedisDict.

Signed-off-by: Roman Gershman <roman@dragonflydb.io>
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Roman Gershman 2022-10-24 13:25:31 +03:00 committed by GitHub
parent 63f8e00273
commit f8f3eac960
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2 changed files with 16 additions and 6 deletions
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14
docs/dense_set.md
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@ -49,9 +49,13 @@ At 100% utilization the Redis dictionary implementation uses approximately 32 by
In comparison using the neighbour cell optimization, `DenseSet` has ~21% of spaces unused at full utilization resulting in $N\*8 + 0.2\*16N \approx 11.2N$ or ~12 bytes per record, yielding ~20 byte savings. The number of bytes per record saved grows as utilization decreases.
Inserting 20M 10 byte strings into a set in chunks of 500 on an i5-8250U give the following results
Command `memtier_benchmark -p 6379 --command "sadd __key__ __data__" -n 10000000 --threads=1 -c 1 --command-key-pattern=R --data-size=10 --key-prefix="key:" --hide-histogram --random-data --key-maximum=1 --randomize --pipeline 20`
produces two sets entries with lots of small records in them.
| | Dragonfly (DenseSet) | Dragonfly (Redis Dictionary) | Redis 7 |
|-------------|----------------------|------------------------------|---------|
| Time | 44.1s | 46.9s | 50.3s |
| Memory used | 626.44MiB | 1.27G | 1.27G |
This is how memory usage looks like with DenseSet:
| Server | Memory (RSS) |
|:---------------------:|:------: |
| Dragonfly/DenseSet | 323MB 🟩 |
| Redis | 586MB |
| Dragonfly/RedisDict | 663MB |

8
src/server/memory_cmd.cc
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@ -47,7 +47,13 @@ void MemoryCmd::Run(CmdArgList args) {
// dummy output, in practice not implemented yet.
return (*cntx_)->SendLong(1);
} else if (sub_cmd == "MALLOC-STATS") {
string res = shard_set->pool()->at(0)->AwaitBrief([this] { return MallocStats(); });
uint32_t tid = 0;
if (args.size() >= 3 && !absl::SimpleAtoi(ArgS(args, 2), &tid)) {
return (*cntx_)->SendError(kInvalidIntErr);
}
tid = tid % shard_set->pool()->size();
string res = shard_set->pool()->at(tid)->AwaitBrief([this] { return MallocStats(); });
return (*cntx_)->SendBulkString(res);
}