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https://issues.apache.org/jira/browse/HADOOP-2585?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Konstantin Shvachko updated HADOOP-2585:
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Attachment: SecondaryStorage.patch
The main features in this patch.
# "-importCheckpoint" argument is introduced for the name-node startup. Started
with this argument
#- The name-node will try to load image from the directory specified in
"fs.checkpoint.dir" and save it to
name-node storage directory(s) set in "dfs.name.dir;
#- The name-node will fail if a legal image is contained in "dfs.name.dir";
#- The name-node verifies that the image in "fs.checkpoint.dir" is consistent,
but does not modify it in any way.
# secondary node storage directory structure is standardized to match the
primary node directory structure.
As a consequence we get protection
#- from accidentally starting multiple secondary nodes in the same directory
#- starting primary and secondary in the same directory.
#- The primary can be started directly with the checkpointed storage if
necessary.
# The checkpoint directory contains now 2 last images: "current" has the most
recent image, and
"previous.checkpoint" has the previous one, which (as I understand it) was
proposed in HADOOP-2987.
# When the checkpoint starts the name-node sends a CheckpointSignature to the
secondary which contains all
important information about the name space: layout version, namespaceID,
creation time, and length of the edits log file.
Information if verified by both nodes, and serves as a confirmation that a) the
image is merged correctly, and
b) that the name-node is receiving the right image when it downloads it back
from the secondary.
We can later extend it this class with fsimage crcs.
# ClientProtocol is changed as a result of that. rollEditLog() returns the
signature instead of just the length of the edits file.
# The primary and Secondary nodes used to have 2 separate servlets for
transferring images.
The problem was that the primary and the secondary were the same
web-application in the servlet container.
I registered secondary under "webapps/secondary" and unified the
GetImageServlet so that it is used for both nodes.
# All logic related to image transferring servlet moved from the NameNode class
directly to FSImage.
# I fixed the bug described in HADOOP-3069.
# TestCheckpoint is substantially modified to cover all new cases of failure.
Particularly, I included the test case for HADOOP-3069, which fails with old
code and does not with the new one.
# StringUtils is extended with getStringCollection(String str) method which
splits of comma delimited string
and returns a collection rather than an array of Strings as getStrings() does.
> Automatic namespace recovery from the secondary image.
> ------------------------------------------------------
>
> Key: HADOOP-2585
> URL: https://issues.apache.org/jira/browse/HADOOP-2585
> Project: Hadoop Core
> Issue Type: New Feature
> Components: dfs
> Affects Versions: 0.15.0
> Reporter: Konstantin Shvachko
> Attachments: SecondaryStorage.patch
>
>
> Hadoop has a three way (configuration controlled) protection from loosing the
> namespace image.
> # image can be replicated on different hard-drives of the same node;
> # image can be replicated on a nfs mounted drive on an independent node;
> # a stale replica of the image is created during periodic checkpointing and
> stored on the secondary name-node.
> Currently during startup the name-node examines all configured storage
> directories, selects the
> most up to date image, reads it, merges with the corresponding edits, and
> writes to the new image back
> into all storage directories. Everything is done automatically.
> If due to multiple hardware failures none of those images on mounted hard
> drives (local or remote)
> are available the secondary image although stale (up to one hour old by
> default) can be still
> used in order to recover the majority of the file system data.
> Currently one can reconstruct a valid name-node image from the secondary one
> manually.
> It would be nice to support an automatic recovery.
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