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https://issues.apache.org/jira/browse/HIVE-18192?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16338020#comment-16338020
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Alan Gates commented on HIVE-18192:
-----------------------------------
I have a question on the design. I don't understand the MIN_HISTORY_LEVEL
table. In the doc it says:
{quote} need this to ensure that we don’t remove TXNS2WRITE_ID data before any
operation that started while this txn was open/aborted is still live. This is
populated when current_txnid starts and locks in its ValidTxnList and the entry
is removed when this txn commits/aborts.
{quote}
Why does this need to be tracked separately? There is already logic to
determine when an entry can be removed from TXN_COMPONENTS and
COMPLETED_TXN_COMPONENTS. Can that not be extended to remove the related entry
from TXNS2WRITE_ID?
> Introduce WriteID per table rather than using global transaction ID
> -------------------------------------------------------------------
>
> Key: HIVE-18192
> URL: https://issues.apache.org/jira/browse/HIVE-18192
> Project: Hive
> Issue Type: Sub-task
> Components: HiveServer2, Transactions
> Affects Versions: 3.0.0
> Reporter: anishek
> Assignee: Sankar Hariappan
> Priority: Major
> Labels: ACID, DR, pull-request-available
> Fix For: 3.0.0
>
> Attachments: HIVE-18192.01.patch, HIVE-18192.02.patch,
> HIVE-18192.03.patch, HIVE-18192.04.patch, HIVE-18192.05.patch
>
>
> To support ACID replication, we will be introducing a per table write Id
> which will replace the transaction id in the primary key for each row in a
> ACID table.
> The current primary key is determined via
> <original transaction id, bucketid , rowid>
> which will move to
> <original write id, bucketid, rowid>
> For each table modified by the given transaction will have a table level
> write ID allocated and a persisted map of global txn id -> to table -> write
> id for that table has to be maintained to allow Snapshot isolation.
> Readers should use the combination of ValidTxnList and
> ValidWriteIdList(Table) for snapshot isolation.
>
> [Hive Replication - ACID
> Tables.pdf|https://issues.apache.org/jira/secure/attachment/12903157/Hive%20Replication-%20ACID%20Tables.pdf]
> has a section "Per Table Sequences (Write-Id)" with more detials
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