Troubleshooting

PXF Errors

The following table describes some errors you may encounter while using PXF:

Error Message	Discussion
Protocol “pxf” does not exist	Cause: The `pxf` extension was not registered. Solution: Create (enable) the PXF extension for the database as described in the PXF Enable Procedure.
Invalid URI pxf://<path-to-data>: missing options section	Cause: The `LOCATION` URI does not include the profile or other required options. Solution: Provide the profile and required options in the URI when you submit the `CREATE EXTERNAL TABLE` command.
PXF server error : Input path does not exist: hdfs://<namenode>:8020/<path-to-file>	Cause: The HDFS file that you specified in <path-to-file> does not exist. Solution: Provide the path to an existing HDFS file.
PXF server error : NoSuchObjectException(message:<schema>.<hivetable> table not found)	Cause: The Hive table that you specified with <schema>.<hivetable> does not exist. Solution: Provide the name of an existing Hive table.
PXF server error : Failed connect to localhost:5888; Connection refused (<segment-id> slice<N> <segment-host>:<port> pid=<process-id>) …	Cause: The PXF Service is not running on <segment-host>. Solution: Restart PXF on <segment-host>.
PXF server error: Permission denied: user=<user>, access=READ, inode="<filepath>":-rw——-	Cause: The Greenplum Database user that ran the PXF operation does not have permission to access the underlying Hadoop service (HDFS or Hive). See Configuring the Hadoop User, User Impersonation, and Proxying.
PXF server error: PXF service could not be reached. PXF is not running in the tomcat container	Cause: The `pxf` extension was updated to a new version but the PXF server has not been updated to a compatible version. Solution: Ensure that the PXF server has been updated and restarted on all hosts.
ERROR: could not load library “/usr/local/greenplum-db-x.x.x/lib/postgresql/pxf.so”	Cause: Some steps have not been completed after a Greenplum Database upgrade or migration, such as `pxf cluster register`. Solution: Make sure you follow the steps outlined for [PXF Upgrade and Migration](https://docs.vmware.com/en/VMware-Greenplum/6/greenplum-database/pxf-pxf_upgrade_migration.html.

Most PXF error messages include a HINT that you can use to resolve the error, or to collect more information to identify the error.

PXF Logging

Refer to the Logging topic for more information about logging levels, configuration, and the pxf-app.out and pxf-service.log log files.

Addressing PXF JDBC Connector Time Zone Errors

You use the PXF JDBC connector to access data stored in an external SQL database. Depending upon the JDBC driver, the driver may return an error if there is a mismatch between the default time zone set for the PXF Service and the time zone set for the external SQL database.

For example, if you use the PXF JDBC connector to access an Oracle database with a conflicting time zone, PXF logs an error similar to the following:

java.io.IOException: ORA-00604: error occurred at recursive SQL level 1
ORA-01882: timezone region not found

Should you encounter this error, you can set default time zone option(s) for the PXF Service in the $PXF_BASE/conf/pxf-env.sh configuration file, PXF_JVM_OPTS property setting. For example, to set the time zone:

export PXF_JVM_OPTS="<current_settings> -Duser.timezone=America/Chicago"

You can use the PXF_JVM_OPTS property to set other Java options as well.

As described in previous sections, you must synchronize the updated PXF configuration to the Greenplum Database cluster and restart the PXF Service on each host.

About PXF External Table Child Partitions

Greenplum Database supports partitioned tables, and permits exchanging a leaf child partition with a PXF external table.

When you read from a partitioned Greenplum table where one or more partitions is a PXF external table and there is no data backing the external table path, PXF returns an error and the query fails. This default PXF behavior is not optimal in the partitioned table case; an empty child partition is valid and should not cause a query on the parent table to fail.

The IGNORE_MISSING_PATH PXF custom option is a boolean that specifies the action to take when the external table path is missing or invalid. The default value is false, PXF returns an error when it encounters a missing path. If the external table is a child partition of a Greenplum table, you want PXF to ignore a missing path error, so set this option to true.

For example, PXF ignores missing path errors generated from the following external table:

CREATE EXTERNAL TABLE ext_part_87 (id int, some_date date)
  LOCATION ('pxf://bucket/path/?PROFILE=s3:parquet&SERVER=s3&IGNORE_MISSING_PATH=true')
FORMAT 'CUSTOM' (formatter = 'pxfwritable_import');

The IGNORE_MISSING_PATH custom option applies only to file-based profiles, including *:text, *:csv, *:fixedwidth, *:parquet, *:avro, *:json, *:AvroSequenceFile, and *:SequenceFile. This option is not available when the external table specifies the hbase, hive[:*], or jdbc profiles, or when reading from S3 using S3-Select.

Addressing Hive MetaStore Connection Errors

The PXF Hive connector uses the Hive MetaStore to determine the HDFS locations of Hive tables. Starting in PXF version 6.2.1, PXF retries a failed connection to the Hive MetaStore a single time. If you encounter one of the following error messages or exceptions when accessing Hive via a PXF external table, consider increasing the retry count:

Failed to connect to the MetaStore Server.
Could not connect to meta store ...
org.apache.thrift.transport.TTransportException: null

PXF uses the hive-site.xml hive.metastore.failure.retries property setting to identify the maximum number of times it will retry a failed connection to the Hive MetaStore. The hive-site.xml file resides in the configuration directory of the PXF server that you use to access Hive.

Perform the following procedure to configure the number of Hive MetaStore connection retries that PXF will attempt; you may be required to add the hive.metastore.failure.retries property to the hive-site.xml file:

Log in to the Greenplum Database coordinator host.
Identify the name of your Hive PXF server.
Open the $PXF_BASE/servers/<hive-server-name>/hive-site.xml file in the editor of your choice, add the hive.metastore.failure.retries property if it does not already exist in the file, and set the value. For example, to configure 5 retries:
```
<property>
    <name>hive.metastore.failure.retries</name>
    <value>5</value>
</property>
```
Save the file and exit the editor.
Synchronize the PXF configuration to all hosts in your Greenplum Database cluster:
```
gpadmin@coordinator$ pxf cluster sync
```
Re-run the failing SQL external table command.

Addressing a Missing Compression Codec Error

By default, PXF does not bundle the LZO compression library. If the Hadoop cluster is configured to use LZO compression, PXF returns the error message Compression codec com.hadoop.compression.lzo.LzoCodec not found on first access to Hadoop. To remedy the situation, you must register the LZO compression library with PXF as described below (for more information, refer to Registering a JAR Dependency):

Locate the LZO library in the Hadoop installation directory on the Hadoop NameNode. For example, the file system location of the library may be /usr/lib/hadoop-lzo/lib/hadoop-lzo.jar.
Log in to the Greenplum Database coordinator host.
Copy hadoop-lzo.jar from the Hadoop NameNode to the PXF configuration directory on the Greenplum Database coordinator host. For example, if $PXF_BASE is /usr/local/pxf-gp6:
```
gpadmin@coordinator$ scp <hadoop-user>@<namenode-host>:/usr/lib/hadoop-lzo/lib/hadoop-lzo.jar /usr/local/pxf-gp6/lib/
```

Synchronize the PXF configuration and restart PXF:

gpadmin@coordinator$ pxf cluster sync
gpadmin@coordinator$ pxf cluster restart

Re-run the query.

Addressing a Snappy Compression Initialization Error

Snappy compression requires an executable temporary directory in which to load its native library. If you are using PXF to read or write a snappy-compressed Avro, ORC, or Parquet file and encounter the error java.lang.NoClassDefFoundError: Could not initialize class org.xerial.snappy.Snappy, the temporary directory used by Snappy (default is /tmp) may not be executable.

To remedy this situation, specify an executable directory for the Snappy tempdir. This procedure involves stopping PXF, updating PXF configuration, synchronizing the configuration change, and then restarting PXF as follows:

Determine if the /tmp directory is executable:
```
$ mount | grep '/tmp'
tmpfs on /tmp type tmpfs (rw,nosuid,nodev,noexec,seclabel)
```
A noexec option in the mount output indicates that the directory is not executable.

Perform this check on each Greenplum Database host.
If the mount command output for /tmp does not include noexec, the directory is executable. Exit this procedure, the workaround will not address your issue.

If the mount command output for /tmp includes noexec, continue.
Log in to the Greenplum Database coordinator host.
Stop PXF on the Greenplum Database cluster:
```
gpadmin@coordinator$ pxf cluster stop
```
Locate the pxf-env.sh file in your PXF installation. If you did not relocate $PXF_BASE, the file is located here:
```
/usr/local/pxf-gp6/conf/pxf-env.sh
```
Open pxf-env.sh in the editor of your choice, locate the line where PXF_JVM_OPTS is set, uncomment the line if it is not already uncommented, and add -Dorg.xerial.snappy.tempdir=${PXF_BASE}/run to the setting. For example:
```
# Memory
export PXF_JVM_OPTS="-Xmx2g -Xms1g -Dorg.xerial.snappy.tempdir=${PXF_BASE}/run"
```
This option sets the Snappy temporary directory to ${PXF_BASE}/run, an executable directory accessible by PXF.

Synchronize the PXF configuration and then restart PXF:

gpadmin@coordinator$ pxf cluster sync
gpadmin@coordinator$ pxf cluster start

Reading from a Hive table STORED AS ORC Returns NULLs

If you are using PXF to read from a Hive table STORED AS ORC and one or more columns that have values are returned as NULLs, there may be a case sensitivity issue between the column names specified in the Hive table definition and those specified in the ORC embedded schema definition. This might happen if the table has been created and populated by another system such as Spark.

The workaround described in this section applies when all of the following hold true:

The Greenplum Database PXF external table that you created specifies the hive:orc profile.
The Greenplum Database PXF external table that you created specifies the VECTORIZE=false (the default) setting.
There is a case mis-match between the column names specified in the Hive table schema and the column names specified in the ORC embedded schema.
You confirm that the field names in the ORC embedded schema are not all in lowercase by performing the following tasks:
1. Run DESC FORMATTED <table-name> in the hive subsystem and note the returned location; for example, location:hdfs://namenode/hive/warehouse/<table-name>.
2. List the ORC files comprising the table by running the following command:
```
$ hdfs dfs -ls <location>
```
3. Dump each ORC file with the following command. For example, if the first step returned hdfs://namenode/hive/warehouse/hive_orc_tbl1, run:
```
$ hive --orcfiledump /hive/warehouse/hive_orc_tbl1/<orc-file> > dump.out
```
4. Examine the output, specifically the value of Type (sample output: Type: struct<COL0:int,COL1:string>). If the field names are not all lowercase, continue with the workaround below.

To remedy this situation, perform the following procedure:

Log in to the Greenplum Database coordinator host.
Identify the name of your Hadoop PXF server configuration.
Locate the hive-site.xml configuration file in the server configuration directory. For example, if $PXF_BASE is /usr/local/pxf-gp6 and the server name is <server_name>, the file is located here:
```
/usr/local/pxf-gp6/servers/<server_name>/hive-site.xml
```

Add or update the following property definition in the hive-site.xml file, and then save and exit the editor:

<property>
    <name>orc.schema.evolution.case.sensitive</name>
    <value>false</value>
    <description>A boolean flag to determine if the comparision of field names in schema evolution is case sensitive.</description>
</property>

Synchronize the PXF server configuration to your Greenplum Database cluster:
```
gpadmin@coordinator$ pxf cluster sync
```
Try the query again.