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From: ctubbsii <git@git.apache.org>
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Subject: [GitHub] accumulo pull request #253: ACCUMULO-4086 Improve volume chooser fallback
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Message-Id: <20170728183736.631A5E02ED@git1-us-west.apache.org>
Date: Fri, 28 Jul 2017 18:37:36 +0000 (UTC)
archived-at: Fri, 28 Jul 2017 18:37:44 -0000

Github user ctubbsii commented on a diff in the pull request:

    https://github.com/apache/accumulo/pull/253#discussion_r130157740
  
    --- Diff: server/base/src/main/java/org/apache/accumulo/server/fs/PerTableVolumeChooser.java ---
    @@ -18,61 +18,146 @@
     
     import java.util.concurrent.ConcurrentHashMap;
     
    -import org.apache.accumulo.core.client.impl.Table;
    +import org.apache.accumulo.core.client.AccumuloException;
    +import org.apache.accumulo.core.conf.AccumuloConfiguration;
     import org.apache.accumulo.core.conf.Property;
     import org.apache.accumulo.server.client.HdfsZooInstance;
     import org.apache.accumulo.server.conf.ServerConfigurationFactory;
     import org.apache.accumulo.server.conf.TableConfiguration;
    +import org.apache.accumulo.start.classloader.vfs.AccumuloVFSClassLoader;
    +import org.slf4j.Logger;
    +import org.slf4j.LoggerFactory;
     
     /**
    - * A {@link VolumeChooser} that delegates to another volume chooser based on the presence of an experimental table property,
    - * {@link Property#TABLE_VOLUME_CHOOSER}. If it isn't found, defaults back to {@link RandomVolumeChooser}.
    + * A {@link VolumeChooser} that delegates to another volume chooser based on other properties: table.custom.volume.chooser for tables, and
    + * general.custom.scoped.volume.chooser for scopes. general.custor.{scope}.volume.chooser can override the system wide setting for
    + * general.custom.scoped.volume.chooser. At the this this was written, the only known scope was "logger".
      */
     public class PerTableVolumeChooser implements VolumeChooser {
    -
    -  private final VolumeChooser fallbackVolumeChooser = new RandomVolumeChooser();
    +  private static final Logger log = LoggerFactory.getLogger(PerTableVolumeChooser.class);
       // TODO Add hint of expected size to construction, see ACCUMULO-3410
       /* Track VolumeChooser instances so they can keep state. */
    -  private final ConcurrentHashMap<Table.ID,VolumeChooser> tableSpecificChooser = new ConcurrentHashMap<>();
    +  private final ConcurrentHashMap<String,VolumeChooser> tableSpecificChooser = new ConcurrentHashMap<>();
    +  private final ConcurrentHashMap<String,VolumeChooser> scopeSpecificChooser = new ConcurrentHashMap<>();
    +  private final RandomVolumeChooser randomChooser = new RandomVolumeChooser();
    +
       // TODO has to be lazily initialized currently because of the reliance on HdfsZooInstance. see ACCUMULO-3411
       private volatile ServerConfigurationFactory serverConfs;
     
    +  public static final String TABLE_VOLUME_CHOOSER = Property.TABLE_ARBITRARY_PROP_PREFIX.getKey() + "volume.chooser";
    +
    +  public static final String SCOPED_VOLUME_CHOOSER(String scope) {
    +    return Property.GENERAL_ARBITRARY_PROP_PREFIX.getKey() + scope + ".volume.chooser";
    +  }
    +
    +  public static final String DEFAULT_SCOPED_VOLUME_CHOOSER = SCOPED_VOLUME_CHOOSER("scoped");
    +
       @Override
    -  public String choose(VolumeChooserEnvironment env, String[] options) {
    -    VolumeChooser chooser = null;
    -    if (env.hasTableId()) {
    -      // This local variable is an intentional component of the single-check idiom.
    -      ServerConfigurationFactory localConf = serverConfs;
    -      if (localConf == null) {
    -        // If we're under contention when first getting here we'll throw away some initializations.
    -        localConf = new ServerConfigurationFactory(HdfsZooInstance.getInstance());
    -        serverConfs = localConf;
    +  public String choose(VolumeChooserEnvironment env, String[] options) throws AccumuloException {
    +    if (log.isTraceEnabled()) {
    +      log.trace("PerTableVolumeChooser.choose");
    +    }
    +    VolumeChooser chooser;
    +    if (!env.hasTableId() && !env.hasScope()) {
    +      // Should only get here during Initialize. Configurations are not yet available.
    +      return randomChooser.choose(env, options);
    --- End diff --
    
    Would it be possible to code init as though it were a proper scope, but not make it configurable? (e.g. always return random chooser if scope == init?)
    
    I'm also thinking that instead of it being "scope || per-table", we have "per-table" treated like a proper scope itself. So, `if scope == per-table: choosePerTable(env.table)`
    
    I can work on this slight refactoring if you're done with your bits, as it's related to the enums we previously discussed.


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