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https://issues.apache.org/jira/browse/CASSANDRA-9666?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Jonathan Ellis updated CASSANDRA-9666:
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Status: Patch Available (was: Open)
> Provide an alternative to DTCS
> ------------------------------
>
> Key: CASSANDRA-9666
> URL: https://issues.apache.org/jira/browse/CASSANDRA-9666
> Project: Cassandra
> Issue Type: Improvement
> Components: Compaction
> Reporter: Jeff Jirsa
> Assignee: Jeff Jirsa
> Fix For: 3.x
>
> Attachments: compactomatic.py, dashboard-DTCS_to_TWCS.png,
> dtcs-twcs-io.png, dtcs-twcs-load.png
>
>
> 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 to a single sstable once that window is no longer current.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 :
> - 2.1: https://github.com/jeffjirsa/cassandra/commits/twcs-2.1
> - 2.2: https://github.com/jeffjirsa/cassandra/commits/twcs-2.2
> - trunk (post-8099): https://github.com/jeffjirsa/cassandra/commits/twcs
> Rebased, force-pushed July 18, with bug fixes for estimated pending
> compactions and potential starvation if more than min_threshold tables
> existed in current window but STCS did not consider them viable candidates
> Rebased, force-pushed Aug 20 to bring in relevant logic from CASSANDRA-9882
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