So i am curious now of how to "unset" the "threshold_ops"-settings in order to allow a upgrade to 5.x index?
I tried setting it to "0" or "NULL" - the first one did not change anything, the 2nd did not work.
Since it is a dynamic setting, i dont think reindexing would be required.
You can update to null an index settings in 5.x series.
In 2.x you have to set it to the default values but I'm unsure if this will solve the problem you are facing.
Can you try with a non production cluster? Create in 2.x an index with that setting and then update to 5.x without changing that setting and see what are the error messages if any.
I tried setting it to the max Int value, no changes.
I set up an 2.4.5 cluster and created the index with the setting, migration plugin showed an error, as expected.
I than upgraded the ES on the server to 5.4.0 and after restart the following logs showed up:
[2017-05-11T11:10:44,358][INFO ][o.e.c.u.IndexFolderUpgrader] [logstash-2016.11.29/1SJ-qAI4SiugEzLx-rfW_Q] upgrading [/es_index/cluster/nodes/0/indices/logstash-2016.11.29] to new naming convention
[2017-05-11T11:10:44,359][INFO ][o.e.c.u.IndexFolderUpgrader] [logstash-2016.11.29/1SJ-qAI4SiugEzLx-rfW_Q] moved from [/es_index/cluster/nodes/0/indices/logstash-2016.11.29] to [/es_index/cluster/nodes/0/indices/1SJ-qAI4SiugEzLx-rfW_Q]
[2017-05-11T11:10:44,465][WARN ][o.e.c.m.MetaDataIndexUpgradeService] [servername] [logstash-2016.11.29/1SJ-qAI4SiugEzLx-rfW_Q] ignoring unknown index setting: [index.translog.flush_threshold_ops] with value [21483647]; archiving
ES did upgrade the index without errors and it still is searchable.
I guess that "solves" my problem here - one can ignore these notifications of the migration plugin.
The "index.translog.flush_threshold_ops" was set before the upgrade to 5.x - the upgrade went fine even tho the migration plugin displayed it otherwise.
After the index was upgraded to 5.x it is no longer possible to set this setting, this message appears:
{"error":{"root_cause":[{"type":"illegal_argument_exception","reason":"unknown setting [index.translog.flush_threshold_ops] did you mean [index.translog.flush_threshold_size]?"}],"type":"illegal_argument_exception","reason":"unknown setting [index.translog.flush_threshold_ops] did you mean [index.translog.flush_threshold_size]?"},
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