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From "Chen Liang (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HDFS-11920) Ozone : add key partition
Date Wed, 19 Jul 2017 00:19:00 GMT

    [ https://issues.apache.org/jira/browse/HDFS-11920?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16092385#comment-16092385

Chen Liang commented on HDFS-11920:

Had an discussion with [~anu] today, mentioned that this key partition across container change
should enable further multi-threading optimization for put/get. Although I think over-partitioned
key is something to avoid, because parallelism also comes with cost. For instance, to write
a key that only has 10 bytes we probably should not try to divide the workload any further.

In the patches, there is a check that a scm block has a configurable max size, say X. This
means if writing is some size Y > X, then the key will be divided into multiple blocks,
each of size X except for last one. I think this just happens to fit the demand for future
parallelism: each thread picks up a size X scm block at a time, write it until all the Y/X
blocks are done. X is the size that we don't bother to over-partition. An alternative can
be having a configurable partition factor, say Z, and given the size Y, we always divide and
make Y/Z partitions, and having Z threads  each picking up one partition. I don't see any
significant difference between these two though.

Anything to add [~anu]?

(Whichever way we decide to go, the actual parallel read/write will need to be added in a
follow-up JIRA.)

> Ozone : add key partition
> -------------------------
>                 Key: HDFS-11920
>                 URL: https://issues.apache.org/jira/browse/HDFS-11920
>             Project: Hadoop HDFS
>          Issue Type: Sub-task
>            Reporter: Chen Liang
>            Assignee: Chen Liang
>         Attachments: HDFS-11920-HDFS-7240.001.patch, HDFS-11920-HDFS-7240.002.patch,
> Currently, each key corresponds to one single SCM block, and putKey/getKey writes/reads
to this single SCM block. This works fine for keys with reasonably small data size. However
if the data is too huge, (e.g. not even fits into a single container), then we need to be
able to partition the key data into multiple blocks, each in one container. This JIRA changes
the key-related classes to support this.

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