apache/hadoop · error · IOException

Unable to retrieve InMemoryAliasMap for block pool id " + bl

Error message

Unable to retrieve InMemoryAliasMap for block pool id " + blockPoolID

What it means

InMemoryLevelDBAliasMapClient iterates its configured InMemoryAliasMapProtocol handles (RPC endpoints from dfs.provided.aliasmap.inmemory.* config) and returns the one whose getBlockPoolId() equals the requested bpid. If no handle matches — including the case where every getBlockPoolId() RPC threw IOException and was only logged as ERROR — this IOException is thrown. Note the swallowing loop: an unreachable alias map server looks identical to a wrong block pool id.

Source

Thrown at hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/common/blockaliasmap/impl/InMemoryLevelDBAliasMapClient.java:173

  private InMemoryAliasMapProtocol getAliasMap(String blockPoolID)
      throws IOException {
    if (blockPoolID == null) {
      throw new IOException("Block pool id required to get aliasmap reader");
    }
    // if a block pool id has been supplied, and doesn't match the associated
    // block pool ids, return null.
    for (InMemoryAliasMapProtocol aliasMap : aliasMaps) {
      try {
        String aliasMapBlockPoolId = aliasMap.getBlockPoolId();
        if (aliasMapBlockPoolId != null &&
            aliasMapBlockPoolId.equals(blockPoolID)) {
          return aliasMap;
        }
      } catch (IOException e) {
        LOG.error("Exception in retrieving block pool id {}", e);
      }
    }
    throw new IOException(
        "Unable to retrieve InMemoryAliasMap for block pool id " + blockPoolID);
  }

  @Override
  public Reader<FileRegion> getReader(Reader.Options opts, String blockPoolID)
      throws IOException {
    InMemoryAliasMapProtocol aliasMap = getAliasMap(blockPoolID);
    LOG.info("Loading InMemoryAliasMapReader for block pool id {}",
        blockPoolID);
    return new LevelDbReader(aliasMap);
  }

  @Override
  public Writer<FileRegion> getWriter(Writer.Options opts, String blockPoolID)
      throws IOException {
    InMemoryAliasMapProtocol aliasMap = getAliasMap(blockPoolID);
    LOG.info("Loading InMemoryAliasMapWriter for block pool id {}",
        blockPoolID);

View on GitHub (pinned to 2add963021)

Solutions

Check the ERROR log line 'Exception in retrieving block pool id' — if present the root cause is the RPC failure there, not the bpid
Verify dfs.provided.aliasmap.inmemory.rpc-address/port point at the running NameNode-side LevelDB alias map service and network/kerberos allows the RPC
Confirm the bpid matches that cluster (compare with the BP-… directory name in the DN's provided/data dirs)
For federation, ensure an alias map endpoint is configured for each nameservice whose blocks the DN serves

Defensive patterns

Strategy: try-catch

Validate before calling

// Preflight: at least one configured alias map must answer for this bpid
boolean found = false;
for (InMemoryAliasMapProtocol p : aliasMapEndpoints) {
  try {
    if (blockPoolID.equals(p.getBlockPoolId())) { found = true; break; }
  } catch (IOException ignored) {
    // endpoint down — surface it instead of silently skipping
  }
}
if (!found) throw new IllegalStateException(
    "No alias map serves block pool " + blockPoolID);

Try / catch

try {
  Reader<FileRegion> r = aliasMapClient.getReader(opts, blockPoolID);
} catch (IOException e) {
  if (e.getMessage() != null && e.getMessage().contains("Unable to retrieve InMemoryAliasMap")) {
    // check the companion ERROR log for RPC failures vs wrong bpid before retrying
  }
  throw e;
}

Prevention

Health-check alias map RPC endpoints as part of cluster validation
In federated setups, keep a mapping of nameservice -> alias map address in config checks

When it happens

Trigger: The blockPoolID belongs to none of the configured remote alias maps, or the alias map RPC endpoints are down/unreachable so their getBlockPoolId() calls fail (see companion ERROR log 'Exception in retrieving block pool id').

Common situations: dfs.provided.aliasmap.inmemory.rpc-address pointing at a dead or wrong service; federation setups where the DN reads with another nameservice's bpid; LevelDB alias map server (in the NN process) not started.

Understand the failure class

Background: 'Could not be found', 'does not exist', 'not found in database': the resource-not-found family when an ID, slug, key, or URI lookup comes back empty — this error's family across 20 libraries.

Related errors

AI-assisted analysis of apache/hadoop@2add963021 (2026-08-22). Data as JSON: /api/errors/0eb39b84045c93b3. Report an issue: GitHub.