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alternator: Update doc regarding tablets support

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Reflect honouring by Alternator the value of the config flag
`tablets_mode_for_new_keyspaces`, as well as renaming of the tag
`experimental:initial_tablets` into `system:initial_tablets`.
This commit is contained in:
Piotr Szymaniak
2025-09-23 16:29:10 +02:00
committed by Nadav Har'El
parent 376a2f2109
commit 35216d2f01
1 changed files with 14 additions and 11 deletions
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25
docs/alternator/new-apis.md
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@@ -181,17 +181,18 @@ entire data center, or other data centers, in that case.
## Tablets
"Tablets" are ScyllaDB's new approach to replicating data across a cluster.
It replaces the older approach which was named "vnodes". Compared to vnodes,
tablets are smaller pieces of tables that are easier to move between nodes,
and allow for faster growing or shrinking of the cluster when needed.
It replaces the older approach which was named "vnodes". See
[Data Distribution with Tablets](../architecture/tablets.rst) for details.
In this version, tablet support is incomplete and not all of the features
which Alternator needs are supported with tablets. So currently, new
Alternator tables default to using vnodes - not tablets.
In this version, tablet support is almost complete, so new
Alternator tables default to following what the global configuration flag
[tablets_mode_for_new_keyspaces](../reference/configuration-parameters.rst#confval-tablets_mode_for_new_keyspaces)
tells them to.
However, if you do want to create an Alternator table which uses tablets,
you can do this by specifying the `experimental:initial_tablets` tag in
the CreateTable operation. The value of this tag can be:
If you want to influence whether a specific Alternator table is created with tablets or vnodes,
you can do this by specifying the `system:initial_tablets` tag
(in earlier versions of Scylla the tag was `experimental:initial_tablets`)
in the CreateTable operation. The value of this tag can be:
* Any valid integer as the value of this tag enables tablets.
Typically the number "0" is used - which tells ScyllaDB to pick a reasonable
@@ -199,9 +200,11 @@ the CreateTable operation. The value of this tag can be:
number overrides the default choice of initial number of tablets.
* Any non-integer value - e.g., the string "none" - creates the table
without tablets - i.e., using vnodes.
without tablets - i.e., using vnodes. However, when vnodes are asked for by the tag value,
but tablets are `enforced` by the `tablets_mode_for_new_keyspaces` configuration flag,
an exception will be thrown.
The `experimental:initial_tablets` tag only has any effect while creating
The `system:initial_tablets` tag only has any effect while creating
a new table with CreateTable - changing it later has no effect.
Because the tablets support is incomplete, when tablets are enabled for an