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From ctubbsii <...@git.apache.org>
Subject [GitHub] accumulo pull request #253: ACCUMULO-4086 Improve volume chooser fallback
Date Tue, 30 May 2017 19:50:57 GMT
Github user ctubbsii commented on a diff in the pull request:

    https://github.com/apache/accumulo/pull/253#discussion_r119197637
  
    --- Diff: server/base/src/main/java/org/apache/accumulo/server/fs/PerTableVolumeChooser.java
---
    @@ -67,86 +69,67 @@ public String choose(VolumeChooserEnvironment env, String[] options)
throws Accu
         return chooser.choose(env, options);
       }
     
    -  private VolumeChooser getVolumeChooserForTable(VolumeChooserEnvironment env, ServerConfigurationFactory
localConf) {
    +  private VolumeChooser getVolumeChooserForTable(VolumeChooserEnvironment env, ServerConfigurationFactory
localConf) throws AccumuloException {
         VolumeChooser chooser;
         if (log.isTraceEnabled()) {
           log.trace("Table id: " + env.getTableId());
         }
         final TableConfiguration tableConf = localConf.getTableConfiguration(env.getTableId());
         String clazz = tableConf.get(Property.TABLE_VOLUME_CHOOSER);
    -    if (null == clazz || clazz.isEmpty()) {
    -      chooser = fallbackVolumeChooser;
    -    } else {
    -      chooser = tableSpecificChooser.get(env.getTableId());
    -      if (chooser == null) {
    -        VolumeChooser temp = Property.createTableInstanceFromPropertyName(tableConf,
Property.TABLE_VOLUME_CHOOSER, VolumeChooser.class, fallbackVolumeChooser);
    -        chooser = tableSpecificChooser.putIfAbsent(env.getTableId(), temp);
    -        if (chooser == null) {
    -          chooser = temp;
    -          // Otherwise, someone else beat us to initializing; use theirs.
    -        }
    -      } else if (!(chooser.getClass().getName().equals(clazz))) {
    -        if (log.isTraceEnabled()) {
    -          log.trace("change detected for table id: " + env.getTableId());
    -        }
    -        // the configuration for this table's chooser has been updated. In the case of
failure to instantiate we'll repeat here next call.
    -        // TODO stricter definition of when the updated property is used, ref ACCUMULO-3412
    -        VolumeChooser temp = Property.createTableInstanceFromPropertyName(tableConf,
Property.TABLE_VOLUME_CHOOSER, VolumeChooser.class, fallbackVolumeChooser);
    -        VolumeChooser last = tableSpecificChooser.replace(env.getTableId(), temp);
    -        if (chooser.equals(last)) {
    -          chooser = temp;
    -        } else {
    -          // Someone else beat us to updating; use theirs.
    -          chooser = last;
    -        }
    -      }
    -    }
    -    return chooser;
    +
    +    return createVolumeChooser(clazz, Property.TABLE_VOLUME_CHOOSER.getKey(), env.getTableId(),
tableSpecificChooser);
       }
     
    -  private VolumeChooser getVolumeChooserForNonTable(VolumeChooserEnvironment env, ServerConfigurationFactory
localConf) {
    +  private VolumeChooser getVolumeChooserForNonTable(VolumeChooserEnvironment env, ServerConfigurationFactory
localConf) throws AccumuloException {
         VolumeChooser chooser;
    -    final String customProperty = Property.GENERAL_ARBITRARY_PROP_PREFIX.getKey() + env.getScope()
+ ".volume.chooser";
    +    String property = VOLUME_CHOOSER_SCOPED_KEY(env.getScope());
     
         if (log.isTraceEnabled()) {
           log.trace("Scope: " + env.getScope());
    -      log.trace("Looking up property: " + customProperty);
    +      log.trace("Looking up property: " + property);
         }
     
         AccumuloConfiguration systemConfiguration = localConf.getConfiguration();
    -    String clazz = systemConfiguration.get(customProperty);
    +    String clazz = systemConfiguration.get(property);
    +    // only if the custom property is not set to we fallback to the table volumn chooser
setting
    +    if (null == clazz) {
    --- End diff --
    
    @ivakegg Ah, yes, we should not be falling back to `table.volume.chooser` for the non-table
scopes. It should simply fail. However, since non-table scopes are a new feature, it might
cause things to fail if the non-table scope delegate hasn't been specified. With that in mind,
I can see how it might be advantageous to consider a single property, rather than fail every
time a new scope is added to the chooser environment.
    
    If we are sticking with the baked-in properties, perhaps: `general.volume.chooser.logger`
and `general.volume.chooser.unknown`. More generally, `general.volume.chooser.<scope>`
    
    If we want to move to custom properties only, perhaps: `table.custom.volume.chooser` instead
of `table.volume.chooser`. And, also the scopes at `general.custom.volume.chooser.<scope>`?
    
    We should also consider how other choosers get their table and non-table configs, rather
than just the `PerTableVolumeChooser`. For example, the `PreferredVolumeChooser` I think gets
its configs from `table.custom.preferredVolumes`, but I'm not sure that makes sense when handling
non-table scopes.
    
    One alternative to the separate properties, which might make it easier to deal with the
various scopes is that we could have more complex property types, whose values include the
class name and its configuration serialized. I haven't thought too hard about what that would
look like, but maybe something structured, like JSON.


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