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https://issues.apache.org/jira/browse/CASSANDRA-6561?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13902223#comment-13902223
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Aleksey Yeschenko commented on CASSANDRA-6561:
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Also, I think we should be doing more extensive validation for cas batches. As
of now, the following batch will execute successfully, assuming t == 5, but
will fail, assuming t == 4.
{code}
begin batch
update foo set z = 1 where x = 'a' and y = 1 if t = 5;
update foo set z = 2 where x = 'a' and y = 2 if t = 4;
apply batch
{code}
Another scenario:
{code}
begin batch
update foo set z = 13 where x = 'a' and y = 1 if z = 23;
update foo set z = 12 where x = 'a' and y = 1 if z = 22;
apply batch
{code}
If z == 23, the batch will succeed. With z == 22 it would not. And even if it
does, 'z' will be set to 12, making it even more confusing/undefined. Such
batches should be rejected.
In other words, we should not allow updating overlapping cells and having
overlapping conditions.
Should also consider the implications of UnsortedColumns replaced by ABSC in
trunk, just in case. (also use addAll in BS.executeWithConditions, b/c
resolve() there is gone).
P.S. Update cqlsh to handle multiple rows returned from a failed CAS batch
updated in bbc56eb60d9c9629deb231131d65cf55ee15c2db.
> 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
> Assignee: Sylvain Lebresne
> Fix For: 2.0.6
>
>
> 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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