It's a possibility. Though I haven't coded and benchmarked such an
approach and I don't think I would have the time before the freeze to
take advantage of the sstable format change opportunity.
Still it's sthg that can be explored later. If we can shave a few extra
% then that would always be great imo.
On 23/6/23 13:57, Benedict wrote:
If we’re doing this, why don’t we delta encode a vint from some per-sstable
minimum value? I’d expect that to commonly compress to a single byte or so.
On 23 Jun 2023, at 12:55, Aleksey Yeshchenko <alek...@apple.com> wrote:
Distant future people will not be happy about this, I can already tell you now.
Sounds like a reasonable improvement to me however.
On 23 Jun 2023, at 07:22, Berenguer Blasi <berenguerbl...@gmail.com> wrote:
Hi all,
DeletionTime.markedForDeleteAt is a long useconds since Unix Epoch. But I
noticed that with 7 bytes we can already encode ~2284 years. We can either shed
the 8th byte, for reduced IO and disk, or can encode some sentinel values (such
as LIVE) as flags there. That would mean reading and writing 1 byte instead of
12 (8 mfda long + 4 ldts int). Yes we already avoid serializing DeletionTime
(DT) in sstables at _row_ level entirely but not at _partition_ level and it is
also serialized at index, metadata, etc.
So here's a POC: https://github.com/bereng/cassandra/commits/ldtdeser-trunk and
some jmh (1) to evaluate the impact of the new alg (2). It's tested here
against a 70% and a 30% LIVE DTs to see how we perform:
[java] Benchmark (liveDTPcParam) (sstableParam) Mode Cnt Score Error
Units
[java] DeletionTimeDeSerBench.testRawAlgReads 70PcLive NC
avgt 15 0.331 ± 0.001 ns/op
[java] DeletionTimeDeSerBench.testRawAlgReads 70PcLive OA
avgt 15 0.335 ± 0.004 ns/op
[java] DeletionTimeDeSerBench.testRawAlgReads 30PcLive NC
avgt 15 0.334 ± 0.002 ns/op
[java] DeletionTimeDeSerBench.testRawAlgReads 30PcLive OA
avgt 15 0.340 ± 0.008 ns/op
[java] DeletionTimeDeSerBench.testNewAlgWrites 70PcLive NC
avgt 15 0.337 ± 0.006 ns/op
[java] DeletionTimeDeSerBench.testNewAlgWrites 70PcLive OA
avgt 15 0.340 ± 0.004 ns/op
[java] DeletionTimeDeSerBench.testNewAlgWrites 30PcLive NC
avgt 15 0.339 ± 0.004 ns/op
[java] DeletionTimeDeSerBench.testNewAlgWrites 30PcLive OA
avgt 15 0.343 ± 0.016 ns/op
That was ByteBuffer backed to test the extra bit level operations impact. But
what would be the impact of an end to end test against disk?
[java] Benchmark (diskRAMParam) (liveDTPcParam) (sstableParam) Mode
Cnt Score Error Units
[java] DeletionTimeDeSerBench.testE2EDeSerializeDT RAM 70PcLive
NC avgt 15 605236.515 ± 19929.058 ns/op
[java] DeletionTimeDeSerBench.testE2EDeSerializeDT RAM 70PcLive
OA avgt 15 586477.039 ± 7384.632 ns/op
[java] DeletionTimeDeSerBench.testE2EDeSerializeDT RAM 30PcLive
NC avgt 15 937580.311 ± 30669.647 ns/op
[java] DeletionTimeDeSerBench.testE2EDeSerializeDT RAM 30PcLive
OA avgt 15 914097.770 ± 9865.070 ns/op
[java] DeletionTimeDeSerBench.testE2EDeSerializeDT Disk 70PcLive
NC avgt 15 1314417.207 ± 37879.012 ns/op
[java] DeletionTimeDeSerBench.testE2EDeSerializeDT Disk
70PcLive OA avgt 15 805256.345 ± 15471.587 ns/op
[java] DeletionTimeDeSerBench.testE2EDeSerializeDT Disk
30PcLive NC avgt 15 1583239.011 ± 50104.245 ns/op
[java] DeletionTimeDeSerBench.testE2EDeSerializeDT Disk
30PcLive OA avgt 15 1439605.006 ± 64342.510 ns/op
[java] DeletionTimeDeSerBench.testE2ESerializeDT RAM
70PcLive NC avgt 15 295711.217 ± 5432.507 ns/op
[java] DeletionTimeDeSerBench.testE2ESerializeDT RAM
70PcLive OA avgt 15 305282.827 ± 1906.841 ns/op
[java] DeletionTimeDeSerBench.testE2ESerializeDT RAM 30PcLive
NC avgt 15 446029.899 ± 4038.938 ns/op
[java] DeletionTimeDeSerBench.testE2ESerializeDT RAM 30PcLive
OA avgt 15 479085.875 ± 10032.804 ns/op
[java] DeletionTimeDeSerBench.testE2ESerializeDT Disk 70PcLive
NC avgt 15 1789434.838 ± 206455.771 ns/op
[java] DeletionTimeDeSerBench.testE2ESerializeDT Disk
70PcLive OA avgt 15 589752.861 ± 31676.265 ns/op
[java] DeletionTimeDeSerBench.testE2ESerializeDT Disk
30PcLive NC avgt 15 1754862.122 ± 164903.051 ns/op
[java] DeletionTimeDeSerBench.testE2ESerializeDT Disk 30PcLive
OA avgt 15 1252162.253 ± 121626.818 ns/o
We can see big improvements when backed with the disk and little impact from
the new alg.
Given we're already introducing a new sstable format (OA) in 5.0 I would like
to try to get this in before the freeze. The point being that sstables with
lots of small partitions would benefit from a smaller DT at partition level. My
tests show a 3%-4% size reduction on disk.
Before proceeding though I'd like to bounce the idea against the community for
all the corner cases and scenarios I might have missed where this could be a
problem?
Thx in advance!
(1)
https://github.com/bereng/cassandra/blob/ldtdeser-trunk/test/microbench/org/apache/cassandra/test/microbench/DeletionTimeDeSerBench.java
(2)
https://github.com/bereng/cassandra/blob/ldtdeser-trunk/src/java/org/apache/cassandra/db/DeletionTime.java#L212
