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https://issues.apache.org/jira/browse/CASSANDRA-6561?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13868013#comment-13868013
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Sylvain Lebresne commented on CASSANDRA-6561:
---------------------------------------------
To quantify my "I think we can support this relatively easily", I've pushed an
initial version of this at https://github.com/pcmanus/cassandra/commits/6561.
I'm calling this an initial version because there is still a few things that I
need to test and it probably lacks a few validations here and there, but I
believe this support pretty much the majority of what we'd want here (that is,
a final version might have a few more lines, but in term of complexity that's
basically it). I've also pushed 2 dtests at
https://github.com/riptano/cassandra-dtest/commit/21fb90e03edcb452feb98027a0272b47de9efb07
that demonstrate the basic functionalities and give a more concrete idea of
how this actually work API wise. I think it's fair to say that while not
trivial, this patch is really not extremely complicated.
I'll note that the patch is against 2.0. That doesn't mean I'm strongly set
with pushing that for 2.0, I'm not. But we did kind of said that we'd try to
support CASSANDRA-5633 use case in 2.0, and since that's what might probably
replace it, I wanted to get a feel of how much code change this would imply for
2.0. If we decide 2.0 is out of question, I'll gladly rebase against trunk.
> Static columns in CQL3
> ----------------------
>
> Key: CASSANDRA-6561
> URL: https://issues.apache.org/jira/browse/CASSANDRA-6561
> Project: Cassandra
> Issue Type: New Feature
> Reporter: Sylvain Lebresne
>
> I'd like to suggest the following idea for adding "static" columns to CQL3.
> I'll note that the basic idea has been suggested by jhalliday on irc but the
> rest of the details are mine and I should be blamed for anything stupid in
> what follows.
> Let me start with a rational: there is 2 main family of CF that have been
> historically used in Thrift: static ones and dynamic ones. CQL3 handles both
> family through the presence or not of clustering columns. There is however
> some cases where mixing both behavior has its use. I like to think of those
> use cases as 3 broad category:
> # to denormalize small amounts of not-entirely-static data in otherwise
> static entities. It's say "tags" for a product or "custom properties" in a
> user profile. This is why we've added CQL3 collections. Importantly, this is
> the *only* use case for which collections are meant (which doesn't diminishes
> their usefulness imo, and I wouldn't disagree that we've maybe not
> communicated this too well).
> # to optimize fetching both a static entity and related dynamic ones. Say you
> have blog posts, and each post has associated comments (chronologically
> ordered). *And* say that a very common query is "fetch a post and its 50 last
> comments". In that case, it *might* be beneficial to store a blog post
> (static entity) in the same underlying CF than it's comments for performance
> reason. So that "fetch a post and it's 50 last comments" is just one slice
> internally.
> # you want to CAS rows of a dynamic partition based on some partition
> condition. This is the same use case than why CASSANDRA-5633 exists for.
> As said above, 1) is already covered by collections, but 2) and 3) are not
> (and
> I strongly believe collections are not the right fit, API wise, for those).
> Also, note that I don't want to underestimate the usefulness of 2). In most
> cases, using a separate table for the blog posts and the comments is The
> Right Solution, and trying to do 2) is premature optimisation. Yet, when used
> properly, that kind of optimisation can make a difference, so I think having
> a relatively native solution for it in CQL3 could make sense.
> Regarding 3), though CASSANDRA-5633 would provide one solution for it, I have
> the feeling that static columns actually are a more natural approach (in term
> of API). That's arguably more of a personal opinion/feeling though.
> So long story short, CQL3 lacks a way to mix both some "static" and "dynamic"
> rows in the same partition of the same CQL3 table, and I think such a tool
> could have it's use.
> The proposal is thus to allow "static" columns. Static columns would only
> make sense in table with clustering columns (the "dynamic" ones). A static
> column value would be static to the partition (all rows of the partition
> would share the value for such column). The syntax would just be:
> {noformat}
> CREATE TABLE t (
> k text,
> s text static,
> i int,
> v text,
> PRIMARY KEY (k, i)
> )
> {noformat}
> then you'd get:
> {noformat}
> INSERT INTO t(k, s, i, v) VALUES ("k0", "I'm shared", 0, "foo");
> INSERT INTO t(k, s, i, v) VALUES ("k0", "I'm still shared", 1, "bar");
> SELECT * FROM t;
> k | s | i | v
> ------------------------------------
> k0 | "I'm still shared" | 0 | "bar"
> k0 | "I'm still shared" | 1 | "foo"
> {noformat}
> There would be a few semantic details to decide on regarding deletions, ttl,
> etc. but let's see if we agree it's a good idea first before ironing those
> out.
> One last point is the implementation. Though I do think this idea has merits,
> it's definitively not useful enough to justify rewriting the storage engine
> for it. But I think we can support this relatively easily (emphasis on
> "relatively" :)), which is probably the main reason why I like the approach.
> Namely, internally, we can store static columns as cells whose clustering
> column values are empty. So in terms of cells, the partition of my example
> would look like:
> {noformat}
> "k0" : [
> (:"s" -> "I'm still shared"), // the static column
> (0:"" -> "") // row marker
> (0:"v" -> "bar")
> (1:"" -> "") // row marker
> (1:"v" -> "foo")
> ]
> {noformat}
> Of course, using empty values for the clustering columns doesn't quite work
> because it could conflict with the user using empty clustering columns. But
> in the CompositeType encoding we have the end-of-component byte that we could
> reuse by using a specific value (say 0xFF, currently we never set that byte
> to anything else than -1, 0 and 1) to indicate it's a static column.
> With that, we'd need to update the CQL3 statements to support the new syntax
> and rules, but that's probably not horribly hard.
> So anyway, this may or may not be a good idea, but I think it has enough meat
> to warrant some consideration.
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