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From "Yang Yang (JIRA)" <j...@apache.org>
Subject [jira] Commented: (CASSANDRA-1982) When creating snapshots, flush isn't required to finish before the snapshots are created
Date Thu, 13 Jan 2011 21:42:46 GMT

    [ https://issues.apache.org/jira/browse/CASSANDRA-1982?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12981499#action_12981499
] 

Yang Yang commented on CASSANDRA-1982:
--------------------------------------

it's probably useful to enable the user to do 2 modes of snapshot:
synchronous and async.

in synchronous snapshot, the snapshot() call should wait for the memtable flushing Callable
object to finish, for all ColumnFamilyStores.

the async mode is just the current implementation.


the semantic for synchronous snapshot means that the resulting snapshot dir will contain all
the data in the system (including memtable and sstables) ***at the exact moment *** that the
user invoked snapshot()

the semantic for async snapshot is that the information contained in the snapshot dir is
from ***some moment **** between when the user invoked snapshot() and when the last time an
sstable was fully dumped

> When creating snapshots, flush isn't required to finish before the snapshots are created
> ----------------------------------------------------------------------------------------
>
>                 Key: CASSANDRA-1982
>                 URL: https://issues.apache.org/jira/browse/CASSANDRA-1982
>             Project: Cassandra
>          Issue Type: Improvement
>          Components: Core
>    Affects Versions: 0.6.9, 0.7.0
>            Reporter: Joaquin Casares
>            Priority: Minor
>
> Right now ColumnFamilyStore.snapshot() works by doing a flush() first, then do symlinks
on the sstables.
> But flush() is actually submitted through Executor, so by the time the code reaches the
symlink part, the flush() may have not happened at all.

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