Github user dyozie commented on a diff in the pull request:
https://github.com/apache/incubator-hawq-docs/pull/94#discussion_r99384586
--- Diff: markdown/pxf/PXFExternalTableandAPIReference.html.md.erb ---
@@ -232,23 +250,23 @@ public class InputData {
### <a id="fragmenter"></a>Fragmenter
-**Note:** The Fragmenter Plugin reads data into HAWQ readable external
tables. The Fragmenter Plugin cannot write data out of HAWQ into writable
external tables.
+**Note:** The Fragmenter class reads data into HAWQ readable external
tables. The Fragmenter class cannot write data out of HAWQ into writable
external tables.
-The Fragmenter is responsible for passing datasource metadata back to
HAWQ. It also returns a list of data fragments to the Accessor or Resolver.
Each data fragment describes some part of the requested data set. It contains
the datasource name, such as the file or table name, including the hostname
where it is located. For example, if the source is a HDFS file, the Fragmenter
returns a list of data fragments containing a HDFS file block. Each fragment
includes the location of the block. If the source data is an HBase table, the
Fragmenter returns information about table regions, including their locations.
+The Fragmenter is responsible for passing datasource metadata back to
HAWQ. It also returns a list of data fragments to the Accessor or Resolver.
Each data fragment describes some part of the requested data set. It contains
the datasource name, such as the file or table name, including the hostname
where it is located. For example, if the source is an HDFS file, the Fragmenter
returns a list of data fragments containing an HDFS file block. Each fragment
includes the location of the block. If the source data is an HBase table, the
Fragmenter returns information about table regions, including their locations.
The `ANALYZE` command now retrieves advanced statistics for PXF readable
tables by estimating the number of tuples in a table, creating a sample table
from the external table, and running advanced statistics queries on the sample
table in the same way statistics are collected for native HAWQ tables.
The configuration parameter `pxf_enable_stat_collection` controls
collection of advanced statistics. If `pxf_enable_stat_collection` is set to
false, no analysis is performed on PXF tables. An additional parameter,
`pxf_stat_max_fragments`, controls the number of fragments sampled to build a
sample table. By default `pxf_stat_max_fragments` is set to 100, which means
that even if there are more than 100 fragments, only this number of fragments
will be used in `ANALYZE` to sample the data. Increasing this number will
result in better sampling, but can also impact performance.
-When a PXF table is analyzed and `pxf_enable_stat_collection` is set to
off, or an error occurs because the table is not defined correctly, the PXF
service is down, or `getFragmentsStats` is not implemented, a warning message
is shown and no statistics are gathered for that table. If `ANALYZE` is running
over all tables in the database, the next table will be processed â a failure
processing one table does not stop the command.
+When a PXF table is analyzed and `pxf_enable_stat_collection` is set to
off, or an error occurs because the table is not defined correctly, the PXF
service is down, or `getFragmentsStats()` is not implemented, a warning message
is shown and no statistics are gathered for that table. If `ANALYZE` is running
over all tables in the database, the next table will be processed â a failure
processing one table does not stop the command.
--- End diff --
This sentence really needs to be unpacked. My best take at it is:
When a PXF table is analyzed, any of the following conditions might result
in a warning message with no statistics gathered for the table:
- `pxf_enable_stat_collection` is set to off, or
- an error occurs because the table is not defined correctly, or
- the PXF service is down, or
- `getFragmentsStats()` is not implemented
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