accumulo-notifications mailing list archives

Site index · List index
Message view « Date » · « Thread »
Top « Date » · « Thread »
From "Josh Elser (JIRA)" <j...@apache.org>
Subject [jira] [Updated] (ACCUMULO-2949) Write explicit "close" markers for WALs
Date Thu, 26 Mar 2015 21:42:53 GMT

     [ https://issues.apache.org/jira/browse/ACCUMULO-2949?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
]

Josh Elser updated ACCUMULO-2949:
---------------------------------
    Assignee:     (was: Josh Elser)

> Write explicit "close" markers for WALs
> ---------------------------------------
>
>                 Key: ACCUMULO-2949
>                 URL: https://issues.apache.org/jira/browse/ACCUMULO-2949
>             Project: Accumulo
>          Issue Type: Improvement
>          Components: logger, replication
>            Reporter: Josh Elser
>
> To ensure that WALs are not left in a dangling "open" state WRT replication, the garbage
collector scans the tablets and constructs a view of WALs that are currently in use. It consults
that view to determine which WALs can move to a "closed" replication state.
> This isn't entirely correct because a WAL can "come back" again after being removed from
a Tablet. Consider the following:
> # Table has one tablet hosted on one tserver
> # Tablet gets some mutations
> # Tablet gets MinC
> # Tablet removes WAL entry as part of MinC
> # WAL is "closed" WRT replication
> # Tablet receives more mutations, starts using the same WAL
> There are a couple of ways that this could present itself, each of which would result
in re-replication of data we've potentially already sent once. On an active system, I don't
think this is of big concern, and we already don't guarantee a "once and only once" replication
contract so this isn't critical. The combiner set on the replication table will also mitigate
most of the re-replication concerns as those records persist until the entire file is replicated
(which should outlast the use on the local system).
> [~ecn] recommended that we could record a "closed" marker for a WAL as a part of {{TabletServerLogger.close()}}
which would prevent the need to "guess" at when a WAL will no longer be used.
> If we want to move to explicit "end" tracking (see ACCUMULO-2835), we will need this
implemented.



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

Mime
View raw message