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f8aaeb5e87
ScyllaDB has special counter columns for which atomic add/subtract
operations like `SET a = a + 1` are allowed. Such operations have not
been allowed on ordinary non-counter columns, as they would not be
properly atomic - the read an the write are separate, and concurrent
operations can have incorrect results.
This patch makes it allowed to use such atomic add/subtract operations
in *LWT* statements. Some examples:
UPDATE ... SET a = a - 1 IF a > 0
UPDATE ... SET a = a + 1 IF EXISTS
UPDATE ... SET a = a + 1 a != NULL
The row updated in the operation, and the updated column (a) should
be initialized before the update - arithmetic operations on missing
column values silently leave the column null (no error is generated).
This add/subtract operations is allowed on any numeric column -
integer or floating point of any size.
The ability of LWT to fetch the old values of a column and use it to
calculate the new value has long been available in our internal CAS
implementation - and has been in use for years in Alternator - but until
this patch it was not exposed in CQL's LWT.
This patch does not add new syntax to CQL - the "SET a = a + b"
and "SET a = a - b" syntax that already existed for counters is now
allowed for non-counters.
This is a new Scylla-only feature that does not exist in Cassandra.
Fixes #10568
Signed-off-by: Nadav Har'El <nyh@scylladb.com>
All tests in this directory and its subdirectories were translated from Apache Cassandra's unit tests - the test/unit/org/apache/cassandra/cql3 directory in the Apache Cassandra source code repository. The organization of this directory mirrors that of the Cassandra directory, with test files renamed from SomeThingTest.java to some_thing_test.py. Individual files were translated in their entirety, and each individual file includes a comment on which version of the file was translated (Cassandra's tests continue to evolve, so we may later want to catch up with the differences). Please avoid adding new tests, not translated from Cassandra, in this directory. Instead, place new tests written from scratch for Scylla, or improved tests, in the directory above.