Downgrade from backup

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1

Hi,

With ES5 released, I wonder whether it would be possible to downgrade to ES2.4 somehow, if something fails?
The exact question is: is it possible to do these steps?

  • in-place (or backup/restore) upgrade from ES2.4 to ES5
  • use ES5 for some time (not using any of its new features, no new indexes or mappings created)
  • backup (from ES5) and restore the data to an ES2.4 cluster
2

No, that's not possible. ES 5.0.0 brings a new major version of Lucene for which the BWC bits are stated as follows (see Section File Formats here):

Older releases are never guaranteed to be able to read indexes generated by newer releases. When this is attempted, a predictable error should be generated.

The Lucene segments written or merged by ES 5.0.0 can't be read by Lucene bundled on ES 2.x.