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https://issues.apache.org/jira/browse/KUDU-3452?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17706674#comment-17706674
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Xixu Wang edited comment on KUDU-3452 at 3/30/23 3:43 AM:
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Thanks very much! [~aserbin]
1. There exists another restriction: (replication_factor + 1) / 2 >= the number
of alive tservers implemented in [https://gerrit.cloudera.org/c/19571]. This
restriction makes sure that RAFT protocol can always elect a leader tablet
replica, so reading and writing data keep available. Therefore, creating a
table with 0 tablet servers will not succeed. And If the table is created
successfully with majority of replicas, it could be able to write into the
newly created table right away.
{color:#c1c7d0}BTW, does it make sense to allow creating a table even with 0
tablet servers available in a cluster? Or the use-case assumes the client
should be able to write into the newly created table right after it gets OK
response for the CreateTable API method?{color}
{color:#172b4d}2. Yes, that is what I mean.{color}
{color:#c1c7d0}Perhaps, by "the risk is the same" you meant the case when one
tablet replica became unavailable after a table has been created in case of
cluster with just 3 nodes.{color}
{color:#172b4d}3. You mean that the table replication factor can not larger
than the total number of tablet servers registered with the catalog manage? I
agree. I will implement it in my commit.{color}
{color:#c1c7d0}But let's please at least check for the total number of tablet
servers registered with the catalog manager{color}
was (Author: wangxixu):
1. There exists another restriction: (replication_factor + 1) / 2 >= the number
of alive tservers implemented in https://gerrit.cloudera.org/c/19571. This
restriction makes sure that RAFT protocol can always elect a leader tablet
replica, so reading and writing data keep available. Therefore, creating a
table with 0 tablet servers will not succeed. And If the table is created
successfully with majority of replicas, it could be able to write into the
newly created table right away.
{color:#c1c7d0}BTW, does it make sense to allow creating a table even with 0
tablet servers available in a cluster? Or the use-case assumes the client
should be able to write into the newly created table right after it gets OK
response for the CreateTable API method?{color}
{color:#172b4d}2. Yes, that is what I mean.{color}
{color:#c1c7d0}Perhaps, by "the risk is the same" you meant the case when one
tablet replica became unavailable after a table has been created in case of
cluster with just 3 nodes.{color}
{color:#172b4d}3. You mean that the table replication factor can not larger
than the total number of tablet servers registered with the catalog manage? I
agree. I will implement it in my commit.{color}
{color:#c1c7d0}But let's please at least check for the total number of tablet
servers registered with the catalog manager{color}
> 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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