Josh Elser created ACCUMULO-2949:
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Summary: 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
Assignee: 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.
If we want to move to explicit "end" tracking (see ACCUMULO-2835), we will need
this implemented.
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