Hoss Man created LUCENE-5126:
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Summary: Codec classes/packages that do not provide (automatic)
file format back should throw an explicit exception
Key: LUCENE-5126
URL: https://issues.apache.org/jira/browse/LUCENE-5126
Project: Lucene - Core
Issue Type: Improvement
Reporter: Hoss Man
If a user builds an index with an alternate codec that does not provide
(automatic) backcompat for reads in future versions of lucene, the resulting
error if the user tries to upgrade can be obscure and missleading -- suggesting
either index corruption or a code bug w/o any obvious indicator that the real
problem is that the user needs to explicitly convert the index format. (Even
if we document the hell out of this -- LUCENE-5125 -- so users have to know
about it when they pick a codec, the person who picked the codec for an app may
be long gone when some other poor sap tries to upgrade that app to use a newer
version of Lucene)
For example, as demonstrated in LUCENE-5121 if a user uses "Disk" based doc
values in 4.2.1, and then tries upgrading to 4.4, they might get...
{noformat}
java.io.EOFException: read past EOF:
MMapIndexInput(path="/home/hossman/tmp/disk_docvals_bug/collection1/data/index/_0_Disk_0.dvdm")
{noformat}
or they might get...
{noformat}
org.apache.lucene.index.CorruptIndexException: invalid type: 65,
resource=MMapIndexInput(path="/storage/solrdata/index/_fd_Disk_0.dvdm")
{noformat}
...it would be a lot better for our users if in situations like this we could
give them a clear and definitive indication (similar to
"IndexFormatTooOldException") that the codec they are using has changed in a
non-backcompat way, and that they need to explicitly convert their index to
supported codec before upgrading.
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