Naive PHB questions to follow... Why are 68y and 20y special? Could you pick any value? Could we allow it to be configurable? (Last one probably overkill, just asking to understand...)
If we can pick any values we want, instinctively I would personally suggest to have TTL higher than 20 years, but also kicking the can further than 2035, which is only 13 years from now. Just to suggest a specific number, why not 35y and 2071? henrik On Fri, Feb 3, 2023 at 12:32 PM Berenguer Blasi <berenguerbl...@gmail.com> wrote: > Hi All, > > a version using Uints, 20y max TTL and kicking the can down the road until > 2086 has been put up for review #justfyi > > Regards > On 15/11/22 7:06, Berenguer Blasi wrote: > > Hi all, > > thanks for your answers!. > > To Benedict's point: In terms of the uvint enconding of deletionTime i.e. > it is true it happens here > https://github.com/apache/cassandra/blob/trunk/src/java/org/apache/cassandra/db/SerializationHeader.java#L170. > But we also have a DeletionTime serializer here > https://github.com/apache/cassandra/blob/trunk/src/java/org/apache/cassandra/db/DeletionTime.java#L166 > that is writing an int and a long that would now write 2 longs. > > TTL itself (the delta) remains an int in the new PR so it should have no > effect in size. > > Did I reference the correct parts of the codebase? No sstable expert here. > On 14/11/22 19:28, Josh McKenzie wrote: > > in 2035 we'd hit the same problem again. > > In terms of "kicking a can down the road", this would be a pretty vigorous > kick. I wouldn't push back against this deferral. :) > > On Mon, Nov 14, 2022, at 9:28 AM, Benedict wrote: > > > I’m confused why we see *any* increase in sstable size - TTLs and deletion > times are already written as unsigned vints as offsets from an sstable > epoch for each value. > > I would dig in more carefully to explore why you’re seeing this increase? > For the same data there should be no change to size on disk. > > > On 14 Nov 2022, at 06:36, C. Scott Andreas <sc...@paradoxica.net> > <sc...@paradoxica.net> wrote: > > A 2-3% increase in storage volume is roughly equivalent to giving up the > gain from LZ4 -> LZ4HC, or a one to two-level bump in Zstandard compression > levels. This regression could be very expensive for storage-bound use cases. > > From the perspective of storage overhead, the unsigned int approach sounds > preferable. > > On Nov 13, 2022, at 10:13 PM, Berenguer Blasi <berenguerbl...@gmail.com> > <berenguerbl...@gmail.com> wrote: > > > > Hi all, > > We have done some more research on c14227. The current patch for > CASSANDRA-14227 solves the TTL limit issue by switching TTL to long instead > of int. This approach does not have a negative impact on memtable memory > usage, as C* controles the memory used by the Memtable, but based on our > testing it increases the bytes flushed by 4 to 7% and the byte on disk by 2 > to 3%. > > As a mitigation to this problem it is possible to encode > *localDeletionTime* as a vint. It results in a 1% improvement but might > cause additional computations during compaction or some other operations. > > Benedict's proposal to keep on using ints for TTL but as a delta to > nowInSecond would work for memtables but not for work in the SSTable where > nowInSecond does not exist. By consequence we would still suffer from the > impact on byte flushed and bytes on disk. > > Another approach that was suggested is the use of unsigned integer. Java 8 > has an unsigned integer API that would allow us to use unsigned int for > TTLs. Based on computation unsigned ints would give us a maximum time of > 136 years since the Unix Epoch and therefore a maximum expiration timestamp > in 2106. We would have to keep TTL at 20y instead of 68y to give us enough > breathing room though, otherwise in 2035 we'd hit the same problem again. > > Happy to hear opinions. > On 18/10/22 10:56, Berenguer Blasi wrote: > > Hi, > > apologies for the late reply as I have been OOO. I have done some > profiling and results look virtually identical on trunk and 14227. I have > attached some screenshots to the ticket > https://issues.apache.org/jira/browse/CASSANDRA-14227. Unless my eyes are > fooling me everything in the jfrs look the same. > > Regards > On 30/9/22 9:44, Berenguer Blasi wrote: > > Hi Benedict, > > thanks for the reply! Yes some profiling is probably needed, then we can > see if going down the delta encoding big refactor rabbit hole is worth it? > > Let's see what other concerns people bring up. > > Thx. > On 29/9/22 11:12, Benedict Elliott Smith wrote: > > My only slight concern with this approach is the additional memory > pressure. Since 64yrs should be plenty at any moment in time, I wonder if > it wouldn’t be better to represent these times as deltas from the nowInSec > being used to process the query. So, long math would only be used to > normalise the times to this nowInSec (from whatever is stored in the > sstable) within a method, and ints would be stored in memtables and any > objects used for processing. > > This might admittedly be more work, but I don’t believe it should be too > challenging - we can introduce a method deletionTime(int nowInSec) that > returns a long value by adding nowInSec to the deletionTime, and make the > underlying value private, refactoring call sites? > > On 29 Sep 2022, at 09:37, Berenguer Blasi <berenguerbl...@gmail.com> > <berenguerbl...@gmail.com> wrote: > > Hi all, > > I have taken a stab in a PR you can find attached in the ticket. Mainly: > > - I have moved deletion times, gc and nowInSec timestamps to long. That > should get us past the 2038 limit. > > - TTL is maxed now to 68y. Think CQL API compatibility and a sort of a > 'free' guardrail. > > - A new NONE overflow policy is the default but everything is backwards > compatible by keeping the previous ones in place. Think upgrade scenarios > or apps relying on the previous behavior. > > - The new limit is around year 292,471,208,677 which sounds ok given the > Sun will start collapsing in 3 to 5 billion years :-) > > - Please feel free to drop by the ticket and take a look at the PR even if > it's cursory > > Thx in advance. > > > -- Henrik Ingo c. +358 40 569 7354 w. www.datastax.com <https://www.facebook.com/datastax> <https://twitter.com/datastax> <https://www.linkedin.com/company/datastax/> <https://github.com/datastax/>
