Known Issues and Workarounds in Impala

The method Impala uses to retrieve the host name while constructing the Kerberos principal is the gethostname() system call. This function might not always return the fully qualified domain name, depending on the network configuration. If the daemons cannot determine the FQDN, Impala does not start on a Kerberized cluster.

Workaround: Test if a host is affected by checking whether the output of the hostname command includes the FQDN. On hosts where hostname, only returns the short name, pass the command-line flag ‑‑hostname=fully_qualified_domain_name in the startup options of all Impala-related daemons.

Apache Issue: IMPALA-4978

Metadata operations that change the state of a table, like COMPUTE STATS or ALTER RECOVER PARTITIONS, may delay metadata propagation of unrelated unloaded tables triggered by statements like DESCRIBE or SELECT queries.

Apache Issue: IMPALA-6671

If the ODBC SQLGetData is called on a series of columns, the function calls must follow the same order as the columns. For example, if data is fetched from column 2 then column 1, the SQLGetData call for column 1 returns NULL.

Apache Issue: IMPALA-1792

Workaround: Fetch columns in the same order they are defined in the table.

Heimdal Kerberos is not supported in Impala.

Apache Issue: IMPALA-7072

Affected Versions: All versions of Impala

Starting in Impala 2.12, Impala, by default, will only allow unencrypted or unauthenticated connections from trusted subnets: 127.0.0.0/8, 10.0.0.0/8, 172.16.0.0/12, 192.168.0.0/16, 169.254.0.0/16. Unencrypted or unauthenticated connections from publicly routable IPs will be rejected.

The trusted subnets can be configured using the --trusted_subnets flag. Set it to '0.0.0.0/0' to allow unauthenticated connections from all remote IP addresses. However, if network access is not otherwise restricted by a firewall, malicious users may be able to gain unauthorized access.

Impala could encounter a serious error due to resource usage under very high concurrency. The error message is similar to:

F0629 08:20:02.956413 29088 llvm-codegen.cc:111] LLVM hit fatal error: Unable to allocate section memory!
terminate called after throwing an instance of 'boost::exception_detail::clone_impl<boost::exception_detail::error_info_injector<boost::thread_resource_error> >'

Apache Issue: IMPALA-5605

Severity: High

Workaround: To prevent such errors, configure each host running an impalad daemon with the following settings:

echo 2000000 > /proc/sys/kernel/threads-max
echo 2000000 > /proc/sys/kernel/pid_max
echo 8000000 > /proc/sys/vm/max_map_count

Add the following lines in /etc/security/limits.conf:

impala soft nproc 262144
impala hard nproc 262144

The size of the breakpad minidump files grows linearly with the number of threads. By default, each thread adds 8 KB to the minidump size. Minidump files could consume significant disk space when the daemons have a high number of threads.

Workaround: Add --minidump_size_limit_hint_kb=size to set a soft upper limit on the size of each minidump file. If the minidump file would exceed that limit, Impala reduces the amount of information for each thread from 8 KB to 2 KB. (Full thread information is captured for the first 20 threads, then 2 KB per thread after that.) The minidump file can still grow larger than the "hinted" size. For example, if you have 10,000 threads, the minidump file can be more than 20 MB.

Apache Issue: IMPALA-3509

Some memory allocated by the JVM used internally by Impala is not counted against the memory limit for the impalad daemon.

Workaround: To monitor overall memory usage, use the top command, or add the memory figures in the Impala web UI /memz tab to JVM memory usage shown on the /metrics tab.

Apache Issue: IMPALA-691

An OUTER JOIN query could omit some expected result rows due to a constant such as FALSE in another join clause. For example:

explain SELECT 1 FROM alltypestiny a1
  INNER JOIN alltypesagg a2 ON a1.smallint_col = a2.year AND false
  RIGHT JOIN alltypes a3 ON a1.year = a1.bigint_col;
+---------------------------------------------------------+
| Explain String                                          |
+---------------------------------------------------------+
| Estimated Per-Host Requirements: Memory=1.00KB VCores=1 |
|                                                         |
| 00:EMPTYSET                                             |
+---------------------------------------------------------+

Apache Issue: IMPALA-3094

Severity: High

If the final character in the RHS argument of a LIKE operator is an escaped \% character, it does not match a % final character of the LHS argument.

Apache Issue: IMPALA-2422

A query could encounter a serious error if includes multiple nested levels of INNER JOIN clauses involving subqueries.

Apache Issue: IMPALA-2603

In Impala 3.2 and higher, if the following error appears multiple times in a short duration while running a query, it would mean that the connection between the impalad and the HDFS NameNode is in a bad state and hence the impalad would have to be restarted:

"hdfsOpenFile() for <filename> at backend <hostname:port> failed to finish before the <hdfs_operation_timeout_sec> second timeout " 

In Impala 3.1 and lower, the same issue would cause Impala to wait for a long time or hang without showing the above error message.

Apache Issue: HADOOP-15720

Affected Versions: All versions of Impala

Workaround: Restart the impalad in the bad state.

This issue can occur either on old Avro tables (created prior to Hive 1.1) or when changing the Avro schema file by adding or removing columns. Columns added to the schema file will not show up in the output of the DESCRIBE FORMATTED command. Removing columns from the schema file will trigger a NullPointerException.

As a workaround, you can use the output of SHOW CREATE TABLE to drop and recreate the table. This will populate the Hive metastore database with the correct column definitions.

ALTER TABLE table_name SET TBLPROPERTIES('EXTERNAL'='TRUE');

Severity: High

For compatibility with Impala, the value for the Flume HDFS Sink hdfs.writeFormat must be set to Text, rather than its default value of Writable. The hdfs.writeFormat setting must be changed to Text before creating data files with Flume; otherwise, those files cannot be read by either Impala or Hive.

Resolution: This information has been requested to be added to the upstream Flume documentation.

The default value in Avro schema must match type of first union type, e.g. if the default value is null, then the first type in the UNION must be "null".

Apache Issue: IMPALA-635

Workaround:Swap the order of the fields in the schema specification. For example, use ["null", "string"] instead of ["string", "null"]. Note that the files written with the problematic schema must be rewritten with the new schema because Avro files have embedded schemas.

If an Avro table has a schema definition with a trailing semicolon, Impala encounters an error when the table is queried.

Apache Issue: IMPALA-1024

Severity: Remove trailing semicolon from the Avro schema.

When comparing a CHAR column value to a string literal, the literal value is not blank-padded and so the comparison might fail when it should match.

Apache Issue: IMPALA-1652

Workaround: Use the RPAD() function to blank-pad literals compared with CHAR columns to the expected length.

A table and a database that share the same name can cause a query failure if the table is not readable by Impala, for example, the table was created in Hive in the Open CSV Serde format. The following exception will return:

CAUSED BY: TableLoadingException: Unrecognized table type for table

Apache Issue: IMPALA-8953

Workaround: Do not create databases and tables with the same names.

Very deeply nested expressions within queries can exceed internal Impala limits, leading to excessive memory usage.

Apache Issue: IMPALA-4551

Severity: High

Workaround: Avoid queries with extremely large expression trees. Setting the query option disable_codegen=true may reduce the impact, at a cost of longer query runtime.

Impala does not support running on clusters with federated namespaces. The impalad process will not start on a node running such a filesystem based on the org.apache.hadoop.fs.viewfs.ViewFs class.

Apache Issue: IMPALA-77

Anticipated Resolution: Limitation

Workaround: Use standard HDFS on all Impala nodes.

If a CREATE TABLE AS SELECT operation successfully creates the target table but an error occurs while querying the source table or copying the data, the new table is left behind rather than being dropped.

Apache Issue: IMPALA-2005

Workaround: Drop the new table manually after a failed CREATE TABLE AS SELECT.

Using a CAST() function to convert large literal values to smaller types, or to convert special values such as NaN or Inf, produces values not consistent with other database systems. This could lead to unexpected results from queries.

Apache Issue: IMPALA-1821

If the LC_* environment variables specify an unsupported locale, Impala does not start.

Apache Issue: IMPALA-532

Workaround: Add LC_ALL="C" to the environment settings for both the Impala daemon and the Statestore daemon. See Modifying Impala Startup Options for details about modifying these environment settings.

Resolution: Fixing this issue would require an upgrade to Boost 1.47 in the Impala distribution.

The extensive logging produced by log level 3 can cause serious performance overhead and capacity issues.

Workaround: Reduce the log level to its default value of 1, that is, GLOG_v=1. See Setting Logging Levels for details about the effects of setting different logging levels.

In catalogd Web UI, you can list metadata objects and view their details. These details are accessed via a link and printed to a string formatted using thrift's DebugProtocol. Printing large objects (> 1 GB) in Web UI can crash catalogd.

Apache Issue: IMPALA-6841