Known Issues in Apache Impala
Learn about the known issues in Impala, the impact or changes to the functionality, and the workaround.
- Impala known limitation when querying compacted tables
- When the compaction process deletes the files for a table from the underlying HDFS
location, the Impala service does not detect the changes as the compactions does not
allocate new write ids. When the same table is queried from Impala it throws a 'File does
not exist' exception that looks something like
Query Status: Disk I/O error on <node>:22000: Failed to open HDFS file hdfs://nameservice1/warehouse/tablespace/managed/hive/<database>/<table>/xxxxx Error(2): No such file or directory Root cause: RemoteException: File does not exist: /warehouse/tablespace/managed/hive/<database>/<table>/xxxx
- Use the REFRESH/INVALIDATE statements on the affected table to overcome the 'File does not exist' exception.
- HADOOP-15720: Queries stuck on failed HDFS calls and not timing out
- 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
impaladand the HDFS NameNode is in a bad state.
In Impala 3.1 and lower, the same issue would cause Impala to wait for a long time or not respond without showing the above error message.
"hdfsOpenFile() for <filename> at backend <hostname:port> failed to finish before the <hdfs_operation_timeout_sec> second timeout "
- Restart the
- IMPALA-532: Impala should tolerate bad locale settings
LC_*environment variables specify an unsupported locale, Impala does not start.
LC_ALL="C"to the environment settings for both the Impala daemon and the Statestore daemon.
- IMPALA-5605: Configuration to prevent crashes caused by thread resource limits
- 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> >'
- To prevent such errors, configure each host running an
impalad daemon with the following settings:
Add the following lines in /etc/security/limits.conf:
echo 2000000 > /proc/sys/kernel/threads-max echo 2000000 > /proc/sys/kernel/pid_max echo 8000000 > /proc/sys/vm/max_map_count
impala soft nproc 262144 impala hard nproc 262144
- IMPALA-635: Avro Scanner fails to parse some schemas
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
- Swap the order of the fields in the schema specification. For
["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.
- IMPALA-691: Process mem limit does not account for the JVM's memory usage
- Some memory allocated by the JVM used internally by Impala is not counted against the memory limit for the impalad daemon.
- 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.
- IMPALA-9350: Ranger audit logs for applying column masking policies missing
- Impala is not producing these logs.
- IMPALA-1024: Impala BE cannot parse Avro schema that contains a trailing semi-colon
- If an Avro table has a schema definition with a trailing semicolon, Impala encounters an error when the table is queried.
- Remove trailing semicolon from the Avro schema.
- IMPALA-1652: Incorrect results with basic predicate on CHAR typed column
- When comparing a
CHARcolumn value to a string literal, the literal value is not blank-padded and so the comparison might fail when it should match.
- Use the
RPAD()function to blank-pad literals compared with
CHARcolumns to the expected length.
- IMPALA-1792: ImpalaODBC: Can not get the value in the SQLGetData(m-x th column) after the SQLBindCol(m th column)
- If the ODBC
SQLGetDatais 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
SQLGetDatacall for column 1 returns
- Fetch columns in the same order they are defined in the table.
- IMPALA-1821: Casting scenarios with invalid/inconsistent results
- Using a
CAST()function to convert large literal values to smaller types, or to convert special values such as
Inf, produces values not consistent with other database systems. This could lead to unexpected results from queries.
- IMPALA-2005: A failed CTAS does not drop the table if the insert fails
- If a
CREATE TABLE AS SELECToperation 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.
- Drop the new table manually after a failed
CREATE TABLE AS SELECT
- IMPALA-2422: % escaping does not work correctly when occurs at the end in a LIKE clause
- If the final character in the RHS argument of a
LIKEoperator is an escaped
\%character, it does not match a
%final character of the LHS argument.
- IMPALA-2603: Crash: impala::Coordinator::ValidateCollectionSlots
- A query could encounter a serious error if includes multiple nested levels of
INNER JOINclauses involving subqueries.
- IMPALA-3094: Incorrect result due to constant evaluation in query with outer join
OUTER JOINquery could omit some expected result rows due to a constant such as
FALSEin 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 | +-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-+
- IMPALA-3509: Breakpad minidumps can be very large when the thread count is high
- 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.
- 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.
- IMPALA-4978: Impala requires FQDN from hostname command on Kerberized clusters
- 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.
- 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_namein the startup options of all Impala-related daemons.
- IMPALA-6671: Metadata operations block read-only operations on unrelated tables
- Metadata operations that change the state of a table, like
ALTER RECOVER PARTITIONS, may delay metadata propagation of unrelated unloaded tables triggered by statements like
- Workaround: None
- IMPALA-7072: Impala does not support Heimdal Kerberos
- CDPD-28139: Set spark.hadoop.hive.stats.autogather to false by default
- As an Impala user, if you submit a query against a table containing data ingested using Spark and you are concerned about the quality of the query plan, you must run COMPUTE STATS against such a table in any case after an ETL operation because numRows created by Spark could be incorrect. Also, use other stats computed by COMPUTE STATS, e.g., Number of Distinct Values (NDV) and NULL count for good selectivity estimates.
- For example, when a user ingests data from a file into a partition of an existing table using Spark, if spark.hadoop.hive.stats.autogather is not set to false explicitly, numRows associated with this partition would be 0 even though there is at least one row in the file. To avoid this, the workaround is to set "spark.hadoop.hive.stats.autogather=false" in the "Spark Client Advanced Configuration Snippet (Safety Valve) for spark-conf/spark-defaults.conf" in Spark's CM Configuration section.
Technical Service Bulletins
- TSB 2021-479: Impala can return incomplete results through JDBC and ODBC clients in all CDP offerings
- In CDP, we introduced a timeout on queries to Impala defaulting to 10 seconds. The timeout setting is called FETCH_ROWS_TIMEOUT_MS. Due to this setting, JDBC, ODBC, and Beeswax clients running Impala queries believe the data returned at 10 seconds is a complete dataset and present it as the final output. However, in cases where there are still results to return after this timeout has passed, when the driver closes the connection, based on the timeout, it results in a scenario where the query results are incomplete.
- Upstream JIRA
- Potential incorrect query results, due to incomplete dataset.
- Action required
- Upgrade (recommended)
- This is fixed in the newest versions of the Impala JDBC driver and the Impala ODBC driver, available at the following locations:
- Impala ODBC 2.6.12 - https://www.cloudera.com/downloads/connectors/impala/odbc/2-6-12.html
- Impala JDBC 2.6.20 - https://www.cloudera.com/downloads/connectors/impala/jdbc/2-6-20.html
Set the property "FETCH_ROWS_TIMEOUT_MS" to 0 if you are unable to use one of the newer versions of the respective drivers listed above. This way, the client can fetch the complete set of data without any issues. Setting the timeout to 0 effectively turns the fetch call into a blocking request which will not timeout and will wait till all the results are fetched. It will wait until all the results come through and/or the network layer timeouts.
This can be set at the Impala server level, or in a pool used with Admission Control, or at the session level, or at the query level.
- On the command line, it can be changed at the server level
- To set the query option at the user session level:
- To set it in admission controls pools via CM:
- Click You will see a screen similar to the following:
- Click Edit and scroll down to Default Query Options.
- Click + and add the query option
FETCH_ROWS_TIMEOUT_MS = 0
- In CDW, users can configure their Impala VW by the following steps:
- Click the three dots and choose the Edit option.
- Select the Impala coordinator tab within the Configurations tab.
- Select flagfile in the drop-down menu.
- Find the default_query_options key and add
the following to the end of the value string:
FETCH_ROWS_TIMEOUT_MS = 0. Make sure to add a comma before adding this to the value string.
- On the command line, it can be changed at the server level as follows:
- Knowledge article
- For the latest update on this issue, see the corresponding Knowledge article: TSB-2021 479: Impala can return incomplete results through JDBC and ODBC clients in all CDP offerings
- TSB 2022-543: Impala query with predicate on analytic function may produce incorrect results
Apache Impala may produce incorrect results for a query which has all of the following conditions:
There are two or more analytic functions (for example,
row_number()) in an inline view
Some of the functions have partition-by expression while the others do not
There is a predicate on the inline view's output expression corresponding to the analytic function
- Upstream JIRA
- Incorrect results returned from certain Impala queries.
- Action required
- Preferred Solution/Upgrade
- Please contact Cloudera Support for raising a Hotfix request until a release with the fix is available.
- Knowledge article
- For the latest update on this issue, see the corresponding Knowledge article: TSB 2022-543: Impala query with predicate on analytic function may produce incorrect results