Logging

PXF provides two categories of message logging: service-level and client-level.

PXF manages its service-level logging, and supports the following log levels (more to less severe):

fatal
error
warn
info
debug
trace

The default configuration for the PXF Service logs at the info and more severe levels. For some third-party libraries, the PXF Service logs at the warn or error and more severe levels to reduce verbosity.

PXF captures messages written to stdout and stderr and writes them to the $PXF_LOGDIR/pxf-app.out file. This file may contain service startup messages that PXF logs before logging is fully configured. The file may also contain debug output.
Messages that PXF logs after start-up are written to the $PXF_LOGDIR/pxf-service.log file.

You can change the PXF log directory if you choose.

Client-level logging is managed by the Greenplum Database client; this topic details configuring logging for a psql client.

Enabling more verbose service-level or client-level logging for PXF may aid troubleshooting efforts.

Configuring the Log Directory

The default PXF logging configuration writes log messages to $PXF_LOGDIR, where the default log directory is PXF_LOGDIR=$PXF_BASE/logs.

To change the PXF log directory, you must update the $PXF_LOGDIR property in the pxf-env.sh configuration file, synchronize the configuration change to the Greenplum Database cluster, and then restart PXF.

Note: The new log directory must exist on all Greenplum Database hosts, and must be accessible by the gpadmin user.

Log in to your Greenplum Database master host:
```
$ ssh gpadmin@<gpmaster>
```
Use a text editor to uncomment the export PXF_LOGDIR line in $PXF_BASE/conf/pxf-env.sh, and replace the value with the new PXF log directory. For example:
```
# Path to Log directory
export PXF_LOGDIR="/new/log/dir"
```
Use the pxf cluster sync command to copy the updated pxf-env.sh file to all hosts in the Greenplum Database cluster:
```
gpadmin@gpmaster$ pxf cluster sync
```
Restart PXF on each Greenplum Database host as described in Restarting PXF.

Configuring Service-Level Logging

PXF utilizes Apache Log4j 2 for service-level logging. PXF Service-related log messages are captured in $PXF_LOGDIR/pxf-app.out and $PXF_LOGDIR/pxf-service.log. The default configuration for the PXF Service logs at the info and more severe levels.

You can change the log level for the PXF Service on a single Greenplum Database host, or on all hosts in the Greenplum cluster.

Note: PXF provides more detailed logging when the debug and trace log levels are enabled. Logging at these levels is quite verbose, and has both a performance and a storage impact. Be sure to turn it off after you have collected the desired information.

Configuring for a Specific Host

You can change the log level for the PXF Service running on a specific Greenplum Database host in two ways:

Setting the PXF_LOG_LEVEL environment variable on the pxf restart command line.
Setting the log level via a property update.

Procedure:

Log in to the Greenplum Database host:
```
$ ssh gpadmin@<gphost>
```
Choose one of the following methods:
- Set the log level on the pxf restart command line. For example, to change the log level from info (the default) to debug:
```
gpadmin@gphost$ PXF_LOG_LEVEL=debug pxf restart
```
- Set the log level in the pxf-application.properties file:
  1. Use a text editor to uncomment the following line in the $PXF_BASE/conf/pxf-application.properties file and set the desired log level. For example, to change the log level from info (the default) to debug:
```
pxf.log.level=debug
```
  2. Restart PXF on the host:
```
gpadmin@gphost$ pxf restart
```
debug logging is now enabled. Make note of the time; this will direct you to the relevant log messages in $PXF_LOGDIR/pxf-service.log.
```
$ date
Wed Oct  4 09:30:06 MDT 2017
$ psql -d <dbname>
```
Perform operations that exercise the PXF Service.
Collect and examine the log messages in pxf-service.log.
Depending upon how you originally set the log level, reinstate info-level logging on the host:
- Command line method:
```
gpadmin@gphost$ pxf restart
```
- Properties file method: Comment out the line or set the property value back to info, and then restart PXF on the host.

Configuring for the Cluster

To change the log level for the PXF service running on every host in the Greenplum Database cluster:

Log in to the Greenplum Database master host:
```
$ ssh gpadmin@<gpmaster>
```
Use a text editor to uncomment the following line in the $PXF_BASE/conf/pxf-application.properties file and set the desired log level. For example, to change the log level from info (the default) to debug:
```
pxf.log.level=debug
```
Use the pxf cluster sync command to copy the updated pxf-application.properties file to all hosts in the Greenplum Database cluster. For example:
```
gpadmin@gpmaster$ pxf cluster sync
```
Restart PXF on each Greenplum Database host:
```
gpadmin@gpmaster$ pxf cluster restart
```
Perform operations that exercise the PXF Service, and then collect and examine the information in $PXF_LOGDIR/pxf-service.log.
Reinstate info-level logging by repeating the steps above with pxf.log.level=info.

Configuring Client-Level Logging

Database-level client session logging may provide insight into internal PXF Service operations.

Enable Greenplum Database client debug message logging by setting the client_min_messages server configuration parameter to DEBUG2 in your psql session. This logging configuration writes messages to stdout, and will apply to all operations that you perform in the session, including operations on PXF external tables. For example:

$ psql -d <dbname>

dbname=# SET client_min_messages=DEBUG2;
dbname=# SELECT * FROM hdfstest;
...
DEBUG2:  churl http header: cell #26: X-GP-URL-HOST: localhost  (seg0 slice1 127.0.0.1:7002 pid=10659)
CONTEXT:  External table pxf_hdfs_textsimple, line 1 of file pxf://data/pxf_examples/pxf_hdfs_simple.txt?PROFILE=hdfs:text
DEBUG2:  churl http header: cell #27: X-GP-URL-PORT: 5888  (seg0 slice1 127.0.0.1:7002 pid=10659)
CONTEXT:  External table pxf_hdfs_textsimple, line 1 of file pxf://data/pxf_examples/pxf_hdfs_simple.txt?PROFILE=hdfs:text
DEBUG2:  churl http header: cell #28: X-GP-DATA-DIR: data%2Fpxf_examples%2Fpxf_hdfs_simple.txt  (seg0 slice1 127.0.0.1:7002 pid=10659)
CONTEXT:  External table pxf_hdfs_textsimple, line 1 of file pxf://data/pxf_examples/pxf_hdfs_simple.txt?PROFILE=hdfs:text
DEBUG2:  churl http header: cell #29: X-GP-TABLE-NAME: pxf_hdfs_textsimple  (seg0 slice1 127.0.0.1:7002 pid=10659)
CONTEXT:  External table pxf_hdfs_textsimple, line 1 of file pxf://data/pxf_examples/pxf_hdfs_simple.txt?PROFILE=hdfs:text
...

Collect and examine the log messages written to stdout.

Note: DEBUG2 database client session logging has a performance impact. Remember to turn off DEBUG2 logging after you have collected the desired information.

dbname=# SET client_min_messages=NOTICE;