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alternator: updated compatibility.md about TTL feature

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The document docs/alternator/compatibility.md suggested that Alternator
does not support the TTL feature at all. The real situation is more
optimistic - this feature is supported, but as experimental feature.
So let's update compatibility.md with the real status of this feature.

Signed-off-by: Nadav Har'El <nyh@scylladb.com>
This commit is contained in:
Nadav Har'El
2022-02-01 16:34:05 +02:00
committed by Botond Dénes
parent 49a8164fb7
commit e06b5d9306
1 changed files with 15 additions and 2 deletions
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docs/alternator/compatibility.md
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@@ -108,8 +108,21 @@ they should be easy to detect. Here is a list of these unimplemented features:
are projected. This wastes some disk space when it is not needed.
https://github.com/scylladb/scylla/issues/5036
* DynamoDB's TTL (per-item expiration) feature is not supported. Note that
this is a different feature from Scylla's feature with the same name.
* DynamoDB's TTL (item expiration) feature is supported, but in this release
still considered experimental and needs to be enabled explicitly with the
`--experimental-features=alternator-ttl` configuration option.
The experimental implementation is mostly complete, but not throughly
tested or optimized.
Like in DynamoDB, Alternator items which are set to expire at a certain
time will not disappear exactly at that time, but only after some delay.
DynamoDB guarantees that the expiration delay will be less than 48 hours
(though for small tables the delay is often much shorter). In Alternator,
the expiration delay is configurable - it defaults to 24 hours but can
be set with the `--alternator-ttl-period-in-seconds` configuration option.
One thing that this implementation is still missing is that expiration
events appear in the Streams API as normal deletions - without the
distinctive marker on deletions which are really expirations.
https://github.com/scylladb/scylla/issues/5060
* DynamoDB's new multi-item transaction feature (TransactWriteItems,