SOLR-8856: Do not cache merge or 'read once' contexts in the hdfs block cache.

solr/CHANGES.txt

@@ -65,9 +65,13 @@ Optimizations
 * SOLR-8722: Don't force a full ZkStateReader refresh on every Overseer operation.
   (Scott Blum via shalin)
   
+* SOLR-8856: Do not cache merge or 'read once' contexts in the hdfs block cache. (Mark Miller)
+
 * SOLR-8745: Deprecate costly ZkStateReader.updateClusterState(), replace with a narrow
   forceUpdateCollection(collection) (Scott Blum via shalin)
   
+* SOLR-8856: Do not cache merge or 'read once' contexts in the hdfs block cache. (Mark Miller, Mike Drob)
+
 Other Changes
 ----------------------
 * SOLR-7516: Improve javadocs for JavaBinCodec, ObjectResolver and enforce the single-usage policy.

solr/core/src/java/org/apache/solr/core/HdfsDirectoryFactory.java

@@ -90,12 +90,19 @@ public class HdfsDirectoryFactory extends CachingDirectoryFactory implements Sol
   
   public static final String CONFIG_DIRECTORY = "solr.hdfs.confdir";
   
+  public static final String CACHE_MERGES = "solr.hdfs.blockcache.cachemerges";
+  public static final String CACHE_READONCE = "solr.hdfs.blockcache.cachereadonce";
+  
   private SolrParams params;
   
   private String hdfsDataDir;
   
   private String confDir;
 
+  private boolean cacheReadOnce;
+
+  private boolean cacheMerges;
+
   private static BlockCache globalBlockCache;
   
   public static Metrics metrics;
@@ -144,6 +151,8 @@ public class HdfsDirectoryFactory extends CachingDirectoryFactory implements Sol
     } else {
       LOG.info(HDFS_HOME + "=" + this.hdfsDataDir);
     }
+    cacheMerges = getConfig(CACHE_MERGES, false);
+    cacheReadOnce = getConfig(CACHE_READONCE, false);
     boolean kerberosEnabled = getConfig(KERBEROS_ENABLED, false);
     LOG.info("Solr Kerberos Authentication "
         + (kerberosEnabled ? "enabled" : "disabled"));
@@ -215,7 +224,7 @@ public class HdfsDirectoryFactory extends CachingDirectoryFactory implements Sol
       
       Cache cache = new BlockDirectoryCache(blockCache, path, metrics, blockCacheGlobal);
       hdfsDir = new HdfsDirectory(new Path(path), lockFactory, conf);
-      dir = new BlockDirectory(path, hdfsDir, cache, null, blockCacheReadEnabled, false);
+      dir = new BlockDirectory(path, hdfsDir, cache, null, blockCacheReadEnabled, false, cacheMerges, cacheReadOnce);
     } else {
       hdfsDir = new HdfsDirectory(new Path(path), lockFactory, conf);
       dir = hdfsDir;

solr/core/src/java/org/apache/solr/store/blockcache/BlockDirectory.java

@@ -92,10 +92,21 @@ public class BlockDirectory extends FilterDirectory implements ShutdownAwareDire
   private final boolean blockCacheReadEnabled;
   private final boolean blockCacheWriteEnabled;
 
+  private boolean cacheMerges;
+  private boolean cacheReadOnce;
+
   public BlockDirectory(String dirName, Directory directory, Cache cache,
       Set<String> blockCacheFileTypes, boolean blockCacheReadEnabled,
       boolean blockCacheWriteEnabled) throws IOException {
+    this(dirName, directory, cache, blockCacheFileTypes, blockCacheReadEnabled, blockCacheWriteEnabled, true, true);
+  }
+  
+  public BlockDirectory(String dirName, Directory directory, Cache cache,
+      Set<String> blockCacheFileTypes, boolean blockCacheReadEnabled,
+      boolean blockCacheWriteEnabled, boolean cacheMerges, boolean cacheReadOnce) throws IOException {
     super(directory);
+    this.cacheMerges = cacheMerges;
+    this.cacheReadOnce = cacheReadOnce;
     this.dirName = dirName;
     blockSize = BLOCK_SIZE;
     this.cache = cache;
@@ -292,6 +303,17 @@ public class BlockDirectory extends FilterDirectory implements ShutdownAwareDire
       return false;
     }
     switch (context.context) {
+      // depending on params, we don't cache on merges or when only reading once
+      case MERGE: {
+        return cacheMerges;
+      }
+      case READ: {
+        if (context.readOnce) {
+          return cacheReadOnce;
+        } else {
+          return true;
+        }
+      }
       default: {
         return true;
       }