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doc: changing topology when changing snitches is no longer supported

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Update the "How to Switch Snitches" document to indicate that changing
topology (i.e. changing node's DC or rack) while changing the snitch is
no longer supported.

Remove a note which said that switching snitches is not supported with
tablets. It was introduced because of the concern that switching a
snitch might change DC or rack of the node, for which our current tablet
load balancer is completely unprepated. Now that changing DC/rack is
forbidden, there doesn't seem to be anything related to snitches which
could cause trouble for tablets.
This commit is contained in:
Piotr Dulikowski
2025-04-17 16:12:12 +02:00
parent 796c8d1601
commit 325a89638c
1 changed files with 3 additions and 25 deletions
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28
docs/operating-scylla/procedures/config-change/switch-snitch.rst
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@@ -1,15 +1,12 @@
How to Switch Snitches
**********************
.. REMOVE IN FUTURE VERSIONS - when the limitation in the note is no longer valid
.. note::
Switching from one type of snitch to another is NOT supported for clusters
where one or more keyspaces have tablets enabled.
NOTE: If you :ref:`create a new keyspace <create-keyspace-statement>`,
it has tablets enabled by default.
Changing the network topology by switching to another type of snitch
is no longer supported. The new snitch must specify the same DC and rack
as the previous one.
This procedure describes the steps that need to be done when switching from one type of snitch to another.
Such a scenario can be when increasing the cluster and adding more data-centers in different locations.
@@ -17,32 +14,13 @@ Snitches are responsible for specifying how ScyllaDB distributes the replicas. T
**Note** - Switching a snitch requires a full cluster shutdown, so It is highly recommended to choose the :doc:`right snitch </operating-scylla/system-configuration/snitch>` for your needs at the cluster setup phase.
+------------------------------------------------------------------------------------+------------------------------------------------------------------------------------+
|Cluster Status |Needed Procedure |
+====================================================================================+====================================================================================+
|No change in network topology |Set the new snitch |
+------------------------------------------------------------------------------------+------------------------------------------------------------------------------------+
|Network topology was changed |Set the new snitch and run repair |
+------------------------------------------------------------------------------------+------------------------------------------------------------------------------------+
Changes in network topology mean that there are changes in the racks or data-centers where the nodes are located.
For example:
**No topology changes**
Original cluster: three nodes cluster on a single data-center with :ref:`Simplesnitch <snitch-simple-snitch>` or :ref:`Ec2snitch <snitch-ec2-snitch>`.
Change to: three nodes in one data-center and one rack using a :ref:`GossipingPropertyFileSnitch <snitch-gossiping-property-file-snitch>` or :ref:`Ec2multiregionsnitch <snitch-ec2-multi-region-snitch>`.
**Topology changes**
Original cluster: three nodes using the :ref:`Simplesnitch <snitch-simple-snitch>` or :ref:`Ec2snitch <snitch-ec2-snitch>` in a single data-center.
Change to: nine nodes in two data-centers using the :ref:`GossipingPropertyFileSnitch <snitch-gossiping-property-file-snitch>` or :ref:`Ec2multiregionsnitch <snitch-ec2-multi-region-snitch>` (add a new data-center).
---------
Procedure
---------