NightOwl888 opened a new pull request #576:
URL: https://github.com/apache/lucenenet/pull/576


   Fixes #573. This is a breaking change. The segment file names were being 
generated in base 10 rather than base 36 (Character.MaxRadix), which caused us 
to generate different segment file names than Lucene and Lucene.NET 3.x. This 
changes the base back to 36, but it means 4.8.0-beta00016 and beyond will not 
be able to read indexes produced by previous betas by default.
   
   To fix this, we added a `SegmentInfos.UseLegacySegmentNames` setting to read 
4.8.0-beta00001 thru 4.8.0-beta00015 indexes, which is `false` by default. 
Setting to `true` at application startup will enable reading indexes from prior 
beta versions (with broken segment names).
   
   > NOTE: We recommend regenerating your indexes, if possible, rather than 
using this "feature". Enabling this makes the file names inconsistent. Some 
methods were generating or parsing in the correct base/radix, but others were 
not. This restores the state to exactly how it was in 4.8.0-beta00015, but do 
note the inconsistency likely means that certain indexes with more than 10 
segments will fail under certain use cases.
   
   ```c#
   SegmentInfos.UseLegacySegmentNames = true;
   ```
   
   Alternatively, set the system property `"useLegacySegmentNames"` to 
`"true"`. Using the default setup, this can be done by adding an environment 
variable named `"lucene:useLegacySegmentNames"` with a value of `"true"`.
   
   The `"useLegacySegmentNames"` setting can be injected by supplying a custom 
`Lucene.Net.Configuration.IConfigurationFactory` using 
`Lucene.Net.Configuration.ConfigurationSettings.SetConfigurationFactory(Configuration.IConfigurationFactory)`.
 See [Configuration Providers in 
.NET](https://docs.microsoft.com/en-us/dotnet/core/extensions/configuration-providers)
 for details about how to configure them. In general there should be 1 
`IConfiguration` per application and it should be passed into the constructor 
of the `IConfigurationFactory` implementation and returned from the 
`IConfigurationFactory.GetConfiguration()` method.
   
   See #307 for more information about system properties.
   
   > NOTE: The prefix "lucene:" only applies to environment variable names, all 
other system property names should exclude this prefix.


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