Alberto Gomez created GEODE-9735:
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Summary: Avoid wan-copy region command to copy entries updated
after it started
Key: GEODE-9735
URL: https://issues.apache.org/jira/browse/GEODE-9735
Project: Geode
Issue Type: Improvement
Components: wan
Reporter: Alberto Gomez
The wan-copy region command must not copy entries that have been created or
updated after the command has started to copy entries.
There are two reasons for this:
* Efficiency: entries copied after the command has been started will be
replicated by the gateway sender anyway so the copying of these entries by the
command will be a waste of processing resources and duplicated events will
arrive to the remote site.
* Problematic reordering of events in the receiving side: if an entry is
modified in the same millisecond in the source site and the wan-copy region
command tries to copy this entry, it might happen that the command reads the
first version of the entry and sends it to the remote site. The gateway sender
will also send two events to the remote site, one with the first version of the
entry and one with the second. If the event of the wan-copy region command
containing the first version of the entry arrives to the remote site after the
second event sent by the gateway sender, it will overwrite the second version
causing an inconsistency between the two sites. The reason is that the
granularity of the timestamp of events is of milliseconds and therefore the
conflict resolver on the receiving side will not be able to detect that the
event sent by the command is prior to the one received by the gateway sender.
If entries updated while the command is running are not copied by the command,
this problem is avoided.
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