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https://issues.apache.org/jira/browse/KUDU-3452?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17702870#comment-17702870
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Alexey Serbin commented on KUDU-3452:
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Having a Kudu cluster with just 3 tablet servers is already quite limiting --
if any of these 3 nodes fail, there isn't a place to replicas which are to
migrate from the failed node. So, a minimum recommended number of tablet
servers nodes is a Kudu cluster is 4 already.
Allowing to create a table with RF=3 when only two tablet servers are alive is
asking for a disaster, because the table's data will become non-available when
just one more node goes down.
Why to create tables with RF=3 then if just a single node failure renders your
data unavailable? You could create tables with RF=1 and have just one tablet
server in your cluster.
> Support creating three-replicas table or partition when only 2 tservers
> healthy
> -------------------------------------------------------------------------------
>
> Key: KUDU-3452
> URL: https://issues.apache.org/jira/browse/KUDU-3452
> Project: Kudu
> Issue Type: Improvement
> Reporter: Xixu Wang
> Priority: Major
>
> h1. Background
> In my case, every day a new Kudu table (called: history_data_table) will be
> created to store history data and a new partition for another table (called:
> business_data_table) to be ready to store today's data. These tables and
> partitions all require 3 replicas. This business logic was implemented by
> some Python scripts. My Kudu cluster contains 3 masters and 3 tservers. Flag:
> --catalog_manager_check_ts_count_for_create_table is false.
> Sometimes, one tserver maybe become unavailable. Table creating task will
> retry continuously and always fail until the tserver become healthy again.
> See the error:
> {color:#ff8b00}E0222 11:10:32.767140 3321 catalog_manager.cc:672] Error
> processing pending assignments: Invalid argument: error selecting replicas
> for tablet 41dffa9783f14f36a5b6c35e89075c1a, state:0: Not enough tablet
> servers are online for table 'test_table'. Need at least 3 replicas, but only
> 2 tablet servers are available{color}
> {color:#172b4d}As there are no enough replicas, a tablet will never be
> created. The state of this tablet is not running. Therefore, read or write
> this tablet will fail even if there are 2 tservers can be used to create 2
> replicas.{color}
>
> An already created tablet can still be on service even if one of its 3
> replicas become unavailable. Why can not create a three-replicas table when
> only 2 tservers healthy?
>
> h1. Design
> A new flag: --support_create_tablet_without_enough_healthy_tservers is added.
> The original logic keeps the same. When this flag is set true, a
> three-replicas tablet can be created successfully and its status is losing
> one replica. This tablet can be be read and write normally.
>
> There are 3 things need to do:
> # A tool to cancel the table creating task.
> # A tool to show the running table creating task.
> # A method to create table without enough healthy tservers
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