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https://issues.apache.org/jira/browse/CASSANDRA-9666?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15110248#comment-15110248
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Antti Nissinen commented on CASSANDRA-9666:
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I agree with Christian, sad to see that the TWCS is not entering the main
stream of Cassandra versions. TWCS provided a clear and consistent behavior of
SStables especially when repair operations are causing a large amount of new
files back in history.
I have to admit that I haven't followed up carefully the latest discussion on
compaction strategies, but I assume that there has been some discussions also
concerning the splitting of SStables according to given time borders that would
also allow the controlled deletion of data from Cassandra so that disk space is
released without the need of compaction of tombstones that will be some day in
future if ever (like in CASSANDRA-10496).
While handling time series data effective deletion of time ranges (all data) is
really important issue and if the Cassandra does not provide that it means that
it has to be build on upper layers using e.g. partitioning to different tables
according to time. Then you can easily drop tables and get rid of old data and
use the latest cassandra versions. However, that causes performance hits and
eats the reputation of Cassandra as usable and manageable time series data
storage engine. Ofcourse using TTL is one solution but it requires that you
can predict future needs in advance. TTL timestamp also increases the space
that each data sample takes on the disk.
> 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
>
> Attachments: 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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