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https://issues.apache.org/jira/browse/CASSANDRA-9666?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14614584#comment-14614584
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Marcus Eriksson commented on CASSANDRA-9666:
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We should not provide 2 different compaction strategies for time series data,
instead we should try to fix the issues you list in DTCS, comments below;
bq. At the present time, DTCS’s first window is compacted using an unusual
selection criteria, which prefers files with earlier timestamps, but ignores
sizes. In TimeWindowCompactionStrategy, the first window data will be compacted
with the well tested, fast, reliable STCS. All STCS options can be passed to
TimeWindowCompactionStrategy to configure the first window’s compaction
behavior.
We should do STCS within all windows, CASSANDRA-9644
bq. HintedHandoff may put old data in new sstables, but it will have little
impact other than slightly reduced efficiency (sstables will cover a wider
range, but the old timestamps will not impact sstable selection criteria during
compaction)
bq. ReadRepair may put old data in new sstables, but it will have little impact
other than slightly reduced efficiency (sstables will cover a wider range, but
the old timestamps will not impact sstable selection criteria during compaction)
This will really hurt read performance if we do this, you will end up hitting
all sstables on disk for every read. The real fix would be to either flush to
several sstables (split by timestamps), or, doing a first special compaction
that writes several sstables into the correct windows.
bq. Small, old sstables resulting from streams of any kind will be swiftly and
aggressively compacted with the other sstables matching their similar
maxTimestamp, without causing sstables in neighboring windows to grow in size.
unsure what you mean here, could you elaborate?
bq. The configuration options are explicit and straightforward - the tuning
parameters leave little room for error. The window is set in common, easily
understandable terms such as “12 hours”, “1 Day”, “30 days”. The
minute/hour/day options are granular enough for users keeping data for hours,
and users keeping data for years.
Yes, DTCS has proven quite difficult to use, CASSANDRA-9645
bq. There is no explicitly configurable max sstable age, though sstables will
naturally stop compacting once new data is written in that window.
Could you elaborate here? How do you avoid old data getting into the windows?
bq. Streaming operations can create sstables with old timestamps, and they'll
naturally be joined together with sstables in the same time bucket. This is
true for bootstrap/repair/sstableloader/removenode.
Unsure what the issue with DTCS is here?
bq. It remains true that if old data and new data is written into the memtable
at the same time, the resulting sstables will be treated as if they were new
sstables, however, that no longer negatively impacts the compaction strategy’s
selection criteria for older windows.
No, but as mentioned above, this will confuse users in other ways, by making
reads very slow
> Provide an alternative to DTCS
> ------------------------------
>
> Key: CASSANDRA-9666
> URL: https://issues.apache.org/jira/browse/CASSANDRA-9666
> Project: Cassandra
> Issue Type: Improvement
> Reporter: Jeff Jirsa
> Assignee: Jeff Jirsa
> Fix For: 2.1.x, 2.2.x
>
>
> DTCS is great for time series data, but it comes with caveats that make it
> difficult to use in production (typical operator behaviors such as bootstrap,
> removenode, and repair have MAJOR caveats as they relate to
> max_sstable_age_days, and hints/read repair break the selection algorithm).
> I'm proposing an alternative, TimeWindowCompactionStrategy, that sacrifices
> the tiered nature of DTCS in order to address some of DTCS' operational
> shortcomings. I believe it is necessary to propose an alternative rather than
> simply adjusting DTCS, because it fundamentally removes the tiered nature in
> order to remove the parameter max_sstable_age_days - the result is very very
> different, even if it is heavily inspired by DTCS.
> Specifically, rather than creating a number of windows of ever increasing
> sizes, this strategy allows an operator to choose the window size, compact
> with STCS within the first window of that size, and aggressive compact down
> to a single sstable once that window is no longer current. The window size is
> a combination of unit (minutes, hours, days) and size (1, etc), such that an
> operator can expect all data using a block of that size to be compacted
> together (that is, if your unit is hours, and size is 6, you will create
> roughly 4 sstables per day, each one containing roughly 6 hours of data).
> The result addresses a number of the problems with
> DateTieredCompactionStrategy:
> - At the present time, DTCS’s first window is compacted using an unusual
> selection criteria, which prefers files with earlier timestamps, but ignores
> sizes. In TimeWindowCompactionStrategy, the first window data will be
> compacted with the well tested, fast, reliable STCS. All STCS options can be
> passed to TimeWindowCompactionStrategy to configure the first window’s
> compaction behavior.
> - HintedHandoff may put old data in new sstables, but it will have little
> impact other than slightly reduced efficiency (sstables will cover a wider
> range, but the old timestamps will not impact sstable selection criteria
> during compaction)
> - ReadRepair may put old data in new sstables, but it will have little impact
> other than slightly reduced efficiency (sstables will cover a wider range,
> but the old timestamps will not impact sstable selection criteria during
> compaction)
> - Small, old sstables resulting from streams of any kind will be swiftly and
> aggressively compacted with the other sstables matching their similar
> maxTimestamp, without causing sstables in neighboring windows to grow in size.
> - The configuration options are explicit and straightforward - the tuning
> parameters leave little room for error. The window is set in common, easily
> understandable terms such as “12 hours”, “1 Day”, “30 days”. The
> minute/hour/day options are granular enough for users keeping data for hours,
> and users keeping data for years.
> - There is no explicitly configurable max sstable age, though sstables will
> naturally stop compacting once new data is written in that window.
> - Streaming operations can create sstables with old timestamps, and they'll
> naturally be joined together with sstables in the same time bucket. This is
> true for bootstrap/repair/sstableloader/removenode.
> - It remains true that if old data and new data is written into the memtable
> at the same time, the resulting sstables will be treated as if they were new
> sstables, however, that no longer negatively impacts the compaction
> strategy’s selection criteria for older windows.
> Patch provided for both 2.1 (
> https://github.com/jeffjirsa/cassandra/commits/twcs-2.1 ) and 2.2 (
> https://github.com/jeffjirsa/cassandra/commits/twcs )
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