`duration` is a new native type that was introduced in Cassandra 3.10 [1].
Support for parsing and the internal representation of the type was added in
8fa47b74e8.
Important note: The version of cqlsh distributed with Scylla does not have
support for durations included (it was added to Cassandra in [2]). To test this
change, you can use cqlsh distributed with Cassandra.
Duration types are useful when working with time-series tables, because they can
be used to manipulate date-time values in relative terms.
Two interesting applications are:
- Aggregation by time intervals [3]:
`SELECT * FROM my_table GROUP BY floor(time, 3h)`
- Querying on changes in date-times:
`SELECT ... WHERE last_heartbeat_time < now() - 3h`
(Note: neither of these is currently supported, though columns with duration
values are.)
Internally, durations are represented as three signed counters: one for months,
for days, and for nanoseconds. Each of these counters is serialized using a
variable-length encoding which is described in version 5 of the CQL native
protocol specification.
The representation of a duration as three counters means that a semantic
ordering on durations doesn't exist: Is `1mo` greater than `1mo1d`? We cannot
know, because some months have more days than others. Durations can only have a
concrete absolute value when they are "attached" to absolute date-time
references. For example, `2015-04-31 at 12:00:00 + 1mo`.
That duration values are not comparable presents some difficulties for the
implementation, because most CQL types are. Like in Cassandra's implementation
[2], I adopted a similar strategy to the way restrictions on the `counter` type
are checked. A type "references" a duration if it is either a duration or it
contains a duration (like a `tuple<..., duration, ...>`, or a UDT with a
duration member).
The following restrictions apply on durations. Note that some of these contexts
are either experimental features (materialized views), or not currently
supported at run-time (though support exists in the parser and code, so it is
prudent to add the restrictions now):
- Durations cannot appear in any part of a primary key, either for tables or
materialized views.
- Durations cannot be directly used as the element type of a `set`, nor can they
be used as the key type of a `map`. Because internal ordering on durations is
based on a byte-level comparison, this property of Cassandra was intended to
help avoid user confusion around ordering of collection elements.
- Secondary indexes on durations are not supported.
- "Slice" relations (<=, <, >=, >) are not supported on durations with `WHERE`
restrictions (like `SELECT ... WHERE span <= 3d`). Multi-column restrictions
only work with clustering columns, which cannot be `duration` due to the
first rule.
- "Slice" relations are not supported on durations with query conditions (like
`UPDATE my_table ... IF span > 5us`).
Backwards incompatibility note:
As described in the documentation [4], duration literals take one of two
forms: either ISO 8601 formats (there are three), or a "standard" format. The ISO
8601 formats start with "P" (like "P5W"). Therefore, identifiers that have this
form are no longer supported.
Fixes#2240.
[1] https://issues.apache.org/jira/browse/CASSANDRA-11873
[2] bfd57d13b7
[3] https://issues.apache.org/jira/browse/CASSANDRA-11871
[4] http://cassandra.apache.org/doc/latest/cql/types.html#working-with-durations
- introcduced "seastarx.hh" header, which does a "using namespace seastar";
- 'net' namespace conflicts with seastar::net, renamed to 'netw'.
- 'transport' namespace conflicts with seastar::transport, renamed to
cql_transport.
- "logger" global variables now conflict with logger global type, renamed
to xlogger.
- other minor changes
More pointedly: Expose columns as is (currently
all_columns_in_select_order), expose name->column mapping more
appropriately named.
Renaming like this is not strictly neccesary, but there is a point to
trying to keep nomenclature similar-ish with origin, esp. when select
order column need to become filtered (spoiler alert).
This changes announce_migration() to return a change event directory in
schema_altering_statement base class. It's needed for drop index
statement, which does not know the keyspace or column family until it
looks up them based on the index. Two stage approach of announcing a
migration and then creating the change event won't work because in the
latter stage, the lookup will fail. The same change in
announce_migration() has been applied to Apache Cassandra.
Use seastar::checked_ptr<weak_ptr<pepared_statement>> instead of shared_ptr for passing prepared statements around.
This allows an easy tracking and handling of statements invalidation.
This implementation will throw an exception every time an invalidated
statement reference is dereferenced.
Signed-off-by: Vlad Zolotarov <vladz@scylladb.com>
This patch adds the MATERIALIZED_VIEWS_FEATURE to the set of cluster
features and requires its presence to allow creating a view. This
ensures view schemas can be safely propagated across nodes.
Signed-off-by: Duarte Nunes <duarte@scylladb.com>
This patchset adds missing properties to the create_view_statement,
such as whether the view is compact or the order of its clustering
columns.
Fixes#1766
This patch uses cf_properties instead to add the missing attributes to
the create_view_statement class.
Fixes#1766
Signed-off-by: Duarte Nunes <duarte@scylladb.com>
This patch extracts the definition of the default compressor into the
compression_parameters class, so that the table and view creation
statements don't have to explicitly deal with it.
Signed-off-by: Duarte Nunes <duarte@scylladb.com>
This patch adds the parsing for the "CREATE MATERIALIZED VIEW" statement,
following Cassandra 3 syntax. For example:
CREATE MATERIALIZED VIEW building_by_city
AS SELECT * FROM buildings
WHERE city IS NOT NULL
PRIMARY KEY(city, name);
It also adds the "IS NOT NULL" operator needed for this purpose.
As in Cassandra, "IS NOT NULL" can only be used for materialized
view creation, and not in a normal SELECT. It can only be used with
the NULL operand (i.e., "IS NOT 3" will be a syntax error).
The current implementation of this statement just does some sanity
checking (such as to verify that "city" is a valid column name and that
the "building" base table exists), complains that materialized views are
not yet supported:
SyntaxException: <ErrorMessage code=2000 [Syntax error in CQL query] message="Failed parsing statement: [CREATE MATERIALIZED VIEW building_by_city AS
SELECT * FROM buildings
WHERE city IS NOT NULL
PRIMARY KEY(city, name);] reason: unsupported operation: Materialized views not yet supported">
As mentioned above, the "IS NOT NULL" restriction is not allowed in
ordinary selects not creating a materialized views:
SELECT * FROM buildings WHERE city IS NOT NULL;
InvalidRequest: code=2200 [Invalid query] message="restriction 'city IS NOT null' is only supported in materialized view creation"
Signed-off-by: Nadav Har'El <nyh@scylladb.com>
Message-Id: <1475742927-30695-1-git-send-email-nyh@scylladb.com>
