[jira] [Resolved] (ACCUMULO-2949) Write explicit "close" markers for WALs

["Christopher Tubbs (JIRA)" <ji...@apache.org>]

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

Christopher Tubbs resolved ACCUMULO-2949.
-----------------------------------------
    Resolution: Invalid

Lots of new WAL improvements have been made in the 1.9.x releases. This is likely OBE. However, please open a new issue at https://github.com/apache/accumulo/issues  if it continues to be a problem.

> 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
>            Priority: Major
>
> 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.



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