hadoop-hdfs-issues mailing list archives

Site index · List index
Message view « Date » · « Thread »
Top « Date » · « Thread »
From "Walter Su (JIRA)" <j...@apache.org>
Subject [jira] [Updated] (HDFS-8501) Erasure Coding: Improve memory efficiency of BlockInfoStriped
Date Sat, 30 May 2015 08:43:17 GMT

     [ https://issues.apache.org/jira/browse/HDFS-8501?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
]

Walter Su updated HDFS-8501:
----------------------------
    Description: 
Erasure Coding: Improve memory efficiency of BlockInfoStriped

Assume we have a BlockInfoStriped:
{noformat}
triplets[] = {s0, s1, s2, s3}
indices[] = {0, 1, 2, 3}
{noformat}

When we run balancer/mover to re-locate replica on s2, firstly it becomes:
{noformat}
triplets[] = {s0, s1, s2, s3, s2}
indices[] = {0, 1, 2, 3, 2}
{noformat}
Then the replica on s2 is removed, finally it becomes:
{noformat}
triplets[] = {s0, s1, null, s3, s2}
indices[] = {0, 1, -1, 3, 2}
{noformat}

The worst case is:
{noformat}
triplets[] = {null, null, null, null, s0, s1, s2, s3}
indices[] = {-1, -1, -1, -1, 0, 1, 2, 3}
{noformat}


We should learn from {{BlockInfoContiguous.removeStorage(..)}}. When a storage is removed,
we bring the last item front.
With the improvement, the worst case become:
{noformat}
triplets[] = {s0, s1, s2, s3, null}
indices[] = {0, 1, 2, 3, -1}
{noformat}
We have an empty slot.

Notes:
Assume we copy 4 storage first, then delete 4. Even with the improvement, the worst case could
be:
{noformat}
triplets[] = {s0, s1, s2, s3, null, null, null, null}
indices[] = {0, 1, 2, 3, -1, -1, -1, -1}
{noformat}
But the Balancer strategy won't move same block/blockGroup twice in a row. So this case is
very rare.

  was:
Erasure Coding: Improve memory efficiency of BlockInfoStriped

Assume we have a BlockInfoStriped:
{noformat}
triplets[] = {s0, s1, s2, s3}
indices[] = {0, 1, 2, 3}
{noformat}

When we run balancer/mover to re-locate replica on s2, firstly it becomes:
{noformat}
triplets[] = {s0, s1, s2, s3, s2}
indices[] = {0, 1, 2, 3, 2}
{noformat}
Then the replica on s1 is removed, finally it becomes:
{noformat}
triplets[] = {s0, s1, null, s3, s2}
indices[] = {0, 1, -1, 3, 2}
{noformat}

The worst case is:
{noformat}
triplets[] = {null, null, null, null, s0, s1, s2, s3}
indices[] = {-1, -1, -1, -1, 0, 1, 2, 3}
{noformat}


We should learn from {{BlockInfoContiguous.removeStorage(..)}}. When a storage is removed,
we bring the last item front.
With the improvement, the worst case become:
{noformat}
triplets[] = {s0, s1, s2, s3, null}
indices[] = {0, 1, 2, 3, -1}
{noformat}
We have an empty slot.

Notes:
Assume we copy 4 storage first, then delete 4. Even with the improvement, the worst case could
be:
{noformat}
triplets[] = {s0, s1, s2, s3, null, null, null, null}
indices[] = {0, 1, 2, 3, -1, -1, -1, -1}
{noformat}
But the Balancer strategy won't move same block/blockGroup twice in a row. So this case is
very rare.


> Erasure Coding: Improve memory efficiency of BlockInfoStriped
> -------------------------------------------------------------
>
>                 Key: HDFS-8501
>                 URL: https://issues.apache.org/jira/browse/HDFS-8501
>             Project: Hadoop HDFS
>          Issue Type: Sub-task
>            Reporter: Walter Su
>            Assignee: Walter Su
>
> Erasure Coding: Improve memory efficiency of BlockInfoStriped
> Assume we have a BlockInfoStriped:
> {noformat}
> triplets[] = {s0, s1, s2, s3}
> indices[] = {0, 1, 2, 3}
> {noformat}
> When we run balancer/mover to re-locate replica on s2, firstly it becomes:
> {noformat}
> triplets[] = {s0, s1, s2, s3, s2}
> indices[] = {0, 1, 2, 3, 2}
> {noformat}
> Then the replica on s2 is removed, finally it becomes:
> {noformat}
> triplets[] = {s0, s1, null, s3, s2}
> indices[] = {0, 1, -1, 3, 2}
> {noformat}
> The worst case is:
> {noformat}
> triplets[] = {null, null, null, null, s0, s1, s2, s3}
> indices[] = {-1, -1, -1, -1, 0, 1, 2, 3}
> {noformat}
> We should learn from {{BlockInfoContiguous.removeStorage(..)}}. When a storage is removed,
we bring the last item front.
> With the improvement, the worst case become:
> {noformat}
> triplets[] = {s0, s1, s2, s3, null}
> indices[] = {0, 1, 2, 3, -1}
> {noformat}
> We have an empty slot.
> Notes:
> Assume we copy 4 storage first, then delete 4. Even with the improvement, the worst case
could be:
> {noformat}
> triplets[] = {s0, s1, s2, s3, null, null, null, null}
> indices[] = {0, 1, 2, 3, -1, -1, -1, -1}
> {noformat}
> But the Balancer strategy won't move same block/blockGroup twice in a row. So this case
is very rare.



--
This message was sent by Atlassian JIRA
(v6.3.4#6332)

Mime
View raw message