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From "Amitanand Aiyer (JIRA)" <j...@apache.org>
Subject [jira] [Updated] (HBASE-4344) Persist memstoreTS to disk
Date Wed, 07 Sep 2011 18:37:09 GMT

     [ https://issues.apache.org/jira/browse/HBASE-4344?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
]

Amitanand Aiyer updated HBASE-4344:
-----------------------------------

    Attachment: patch-2

There are three parts to the changes made here:
 
The first one is in the write path, while writing the HFile (V2). We include the memstoreTS
along with the other information already written during the KeyValue.

We maintain and append to the file info the maximum memstoreTS found among all the key-values
written to the disk. The presence of this information in the file info represents the fact
that the Key-values written to the HFile is in the new format that includes the memstoreTS.

Part 2: The reader is modified accordingly to see if the file info suggests the presence of
the memstoreTS or not. If it does, then we also read the memstoreTS while preparing the KeyValues
in the reader.

Part 3: On Region open/initialize, we need to ensure that the RWCC is initialized with a value
bigger than the max of any value found in the storeFiles. this is necessary to ensure that
the writes in the storefiles are seen by future reads.

> Persist memstoreTS to disk
> --------------------------
>
>                 Key: HBASE-4344
>                 URL: https://issues.apache.org/jira/browse/HBASE-4344
>             Project: HBase
>          Issue Type: Sub-task
>            Reporter: Amitanand Aiyer
>            Assignee: Amitanand Aiyer
>             Fix For: 0.89.20100924
>
>         Attachments: patch-2
>
>
> Atomicity can be achieved in two ways -- (i) by using  a multiversion concurrency system
(MVCC), or (ii) by ensuring that "new" writes do not complete, until the "old" reads complete.
> Currently, Memstore uses something along the lines of MVCC (called RWCC for read-write-consistency-control).
But, this mechanism is not incorporated for the key-values written to the disk, as they do
not include the memstore TS.
> Let us make the two approaches be similar, by persisting the memstoreTS along with the
key-value when it is written to the disk.

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