You can write data out of s-Server to a file in Hadoop/HDFS from a stream or table. The Hadoop ECDA adapter automatically uploads a file to a designated Hadoop file system location designated by the HDFS_OUTPUT_DIR property. s-Server implements an HDFS client to connect to an HDFS server.
s-Server formats files for HDFS according to the same principles as it does for writing to the file system. See Writing to the File System for more details. You can specify how files rotate according to time, size, or both, and you can specify how rotated files are named.
To write from local locations, you configure and launch the adapter in SQL, using either server or foreign stream/table options. See Writing to HDFS Using SQL below. To write from remote locations, you configure such options using a properties file and launch the agent at the command line. See Writing to HDFS Using the ECD Agent below.
Files can be formatted as CSV, Avro, XML, JSON, or BSON. These files do not require further formatting in order to be integrated with Hadoop. (Once in the Hadoop file system, these files will be accessed by second-level systems such as Hive. See https://cwiki.apache.org/confluence/display/Hive/Home for more details on Hive.)
For adapters, you configure and launch the adapter in SQL, using either server or foreign stream/table options. For more information on creating foreign streams, see the topic CREATE FOREIGN STREAM in the Streaming SQL Reference Guide.
To write data to HDFS, you need to create a foreign stream that references the prebuilt server object HDFS_SERVER.
Required parameters are:
All foreign streams must be created within a schema. The following code first creates a schema in which to run the rest of the sample code below, then creates a foreign stream named hadoopschema.hdfssink.
CREATE OR REPLACE SCHEMA hadoop_schema; SET SCHEMA 'hadoop_schema'; CREATE or REPLACE FOREIGN STREAM hadoop_schema.hdfs_sink ( "id" INTEGER, "shift_no" DOUBLE, "reported_at" TIMESTAMP NOT NULL, "trip_no" VARCHAR(10), "latitude" DOUBLE, "longitude" DOUBLE, "speed" INTEGER, "baring" INTEGER, "active" BOOLEAN) --built-in server object for HDFS SERVER HDFS_SERVER OPTIONS ( "CONFIG_PATH" '/home/mydirectory/default.xml', "AUTH_METHOD" 'kerberos', "AUTH_USERNAME" 'nn/hadoop.docker.com@EXAMPLE.COM', "AUTH_KEYTAB" '/tmp/nn.service.keytab', "HDFS_OUTPUT_DIR" 'hdfs://storm-s3.disruptivetech.com:8020/user/sqlstream/', "FORMATTER" 'CSV', "QUOTE_CHARACTER" '', "SEPARATOR" ',', "WRITE_HEADER" 'false', "DIRECTORY" '/tmp', "ORIGINAL_FILENAME" 'bus-output.csv', "FILENAME_PREFIX" 'output-', "FILENAME_SUFFIX" '.csv', "FILENAME_DATE_FORMAT" 'yyyy-MM-dd-HH:mm:ss', "FILE_ROTATION_SIZE" '20K' "FORMATTER_INCLUDE_ROWTIME" 'true');
To begin writing data to Hadoop with the above code, you INSERT into hadoop_schema.hdfs_sink. When hadoop_schema.hdfs_sink receives rows, s-Server writes data to the Hadoop server you have configured in the foreign stream options.
In most cases, you will want to set up a pump that writes data to _hadoopschema.hdfs_sink. Pumps are INSERT macros that continually pass data from one point in a streaming pipeline to the other. See the topic CREATE PUMP in the s-Server Streaming SQL Reference Guide for more details.
You do so with code along the following lines:
CREATE OR REPLACE SCHEMA Pumps; SET SCHEMA 'Pumps'; CREATE OR REPLACE PUMP writerPump STOPPED AS --We recommend creating pumps as stopped --then using ALTER PUMP "Pumps"."writerPump" START to start it INSERT INTO hadoop_schema.hdfs_sink SELECT STREAM * FROM "MyStream"; --where "MyStream" is a currently existing stream
To start writing data, use the following code:
ALTER PUMP Pumps.writerPump START;
You configure adapter options through foreign streams/tables. You configure agent options through the ECD agent property file.
The following options are specific to HDFS:
|AUTH_METHOD||Optional. If desired, specify 'kerberos' Requires AUTH_USERNAME and AUTH_KEYTAB (the latter should be implemented using JNDI properties. See Hadoop Options for Use with JNDI Properties below|
|AUTH_USERNAME||User name for HDFS. Required if AUTH_METHOD is specified.|
|HDFS_OUTPUT_DIR||Address for name node of HDFS, such as hdfs://storm-s3.disruptivetech.com:8020/user/sqlstream/. This is where data will be written to on the HDFS server.|
|CONFIG_PATH||Optional. Specifies path to an HDFS client configuration file. This will be loaded and used by s-Server's HDFS client in it’s entire life cycle. Example: /home/me/work/kerberos/core-default.xml|
|AUTH_KEYTAB||Path to file containing pairs of Kerberos principals and encrypted keys, such as /tmp/nn.service.keytab Required if AUTH_METHOD is specified.|
|HIVE_TABLE_NAME||Defaults to null. Table name inside HIVE_SCHEMA_NAME.|
|HIVE_SCHEMA_NAME||Defaults to null. Schema (database) containing the table. Must be specified if HIVE_TABLE_NAME is specified.|
|AUTH_METASTORE_PRINCIPAL||Defaults to null. Required if HIVE_TABLE_NAME is specified. 3-part name of the Kerberos principal which can read the Hive metastore. This is the value of the hive.metastore.kerberos.principal property set in the Hive installation's hive-site.xml descriptor file.|
|HIVE_URI||Defaults to null. JDBC URL for accessing the Hive server when loading data into Hive tables. Must be specified if HIVE_TABLE_NAME is specified.|
|HIVE_METASTORE_URIS||Defaults to null. Location of the Hive metastore for loading data into Hive tables. Required if HIVE_TABLE_NAME is specified.|
|$columnName_HIVE_PARTITION_NAME_FORMAT||This option specifies custom formatting directives for partition key values when they are used to construct the names of HDFS directory levels. $columnName must be the name of a partition key of type DATE or TIMESTAMP. The value bound to this option must be a valid format string as understood by java.text.SimpleDateFormat.|
|OPTIONS_QUERY||Optional. Lets you query a table to update one or more adapter options at runtime. You can use this, for example, to set the HDFS_OUTPUT_DIR option from a table that contains options, as in
We recommend that you supply any options related to access credentials, such as those for SSL or Kerberos credentials, using the following .properties files:
The following options apply to all file-based sinks.
Note: When you specify DIRECTORY with a Hadoop sink, this location refers to where s-Server writes data locally before copying it to HDFS.
|DIRECTORY||Directory to which you are writing. s-Server needs permission to write to this directory.|
|ORIGINAL_FILENAME||Name of file to write before rotation. This will be the name of the file that s-Server is currently writing.|
|FILENAME_PREFIX||Prefix of the final output file name, such as "test-".|
|FILENAME_DATE_FORMAT||Java time format to use in the final output file name, for example yyyy-MM-dd_HH:mm:ss. Uses java SimpleDateFormat. This specifies how to format a timestamp that appears between the prefix and the suffix. This timestamp is the ROWTIME of the last row in the file.|
|FILE_ROTATION_WATERMARK_COLUMN||This declares the name of a source column whose contents will be used to further distinguish files in the series.|
|FILENAME_SUFFIX||Suffix of the final output file name. If you want this suffix to include a period, you must specify it, e.g. ".csv"|
|FILE_ROTATION_TIME||Determines when files rotate based on time elapsed since Unix epoch time. Defaults to 0. That means "don't use ROWTIME to trigger file rotation". You must specify either FILE_ROTATION_TIME or FILE_ROTATION_SIZE as an option. You can choose to specify both. You set FILE_ROTATION_TIME as a positive integer with a unit of either milliseconds (ms), seconds (s), minutes (m), hours (h), or days (d) - for example '15s', '20m', '2h' or '3d'. These express intervals of time from 1970-01-01; files rotate once a row arrives with a ROWTIME that passes the specified interval. See Using FILE_ROTATION_TIME.|
|FILE_ROTATION_SIZE||Determines when files rotate based on file size. s-Server rotates to the next file once a row arrives that brings the file size over the byte threshhold specified by FILE_ROTATION_SIZE. You must specify either FILE_ROTATION_TIME or FILE_ROTATION_SIZE. You can choose to specify both. Lets you specify a file size in kilobytes (k), megabytes (m), or gigabytes (g). Expressed as a positive integer followed by a byte measurement, for example '64k', '100m', '8g'. Defaults to 0 - which means "don't use file size to trigger file rotation". See Using FILE_ROTATION_SIZE.|
|FILE_ROTATION_RESPECT_ROWTIME||'true' or 'false', case-insensitive. When you use FILE_ROTATION_SIZE, this option lets you specify whether files wait to rotate until all rows with the same ROWTIME have arrived. Defaults to 'true', which means "always respect rowtime". See Using FILE_ROTATION_RESPECT_ROWTIME.|
|ESCAPE_<column name>||True or false; defaults to true. Causes strings to be escaped before being written.|
|POSTPROCESS_COMMAND||The POSTPROCESS_COMMAND option lets you run a script after each output file is written. To use this option, enter the path to the script, along with any parameters needed by the script, substituting <input> for the name of the file. When the file is complete, the script will execute with parameters, and <input> will be replaced by the name of the file.
Example: '/home/sqlstream/scripts/send-to-destination.sh <input> sftp://some.sftp.server.com'
s-Server rotates files according to options set for FILE_ROTATION_TIME, FILE_ROTATION_SIZE and FILE_ROTATION_RESPECT_ROWTIME.
File rotation options work together in the following ways:
Rotate the file if (the FILE_ROTATION_TIME condition is satisfied OR the FILE_ROTATION_SIZE condition is satisfied) AND (the FILE_ROTATION_RESPECT_ROWTIME condition is satisfied).
You can use FILE_ROTATION_TIME to rotate files based on time elapsed since Unix epoch time. You set FILE_ROTATION_TIME as a positive integer with a unit of either milliseconds (ms), seconds (s), minutes (m), hours (h), or days (d). These express intervals of time from 1970-01-01: an interval might be 15 minutes, 1 hour, or 1 day. Files rotate once a row arrives with a ROWTIME that passes the specified interval.
More technically, FILE_ROTATION_TIME works as follows:
s-Server rotates to the next file when:
You can use FILE_ROTATION_SIZE to rotate files based on their size. You specify a file size in kilobytes (k), megabytes (m), or gigabytes (g). Expressed as a positive integer followed by a byte measurement: Defaults to 0. That means "don't use file size to trigger file rotation".
Note: You cannot use FILE_ROTATION_SIZE for writing to Hive tables.
When using FILE_ROTATION_SIZE, you can specify that files wait to rotate until all rows with the same ROWTIME have arrived. See FILE_ROTATION_RESPECT_ROWTIME below.
Setting FILE_ROTATION_RESPECT_ROWTIME to true ensures that rows with the same rowtime will not be split between two files. For example, if you have set FILE_ROTATION_SIZE to 1m (1 megabyte), and a new row arrives that causes the file to go over the 1 megabyte threshold, if FILE_ROTATION_RESPECT_ROWTIME is set to true, s-Server waits until all rows with the same ROWTIME have arrived. That is, s-Server waits until a new row arrives with a different ROWTIME, even if accepting rows with the same ROWTIME causes the file to grow larger than 1 megabyte.
If you set FILE_ROTATION_RESPECT_ROWTIME to true, you cannot write files from tables, whose rows lack rowtimes. s-Server will raise an error if you try to insert into a file writer foreign stream that has FILE_ROTATION_RESPECT_ROWTIME set to true. That means that if you are planning to write rows from a table into a file, you must set FILE_ROTATION_RESPECT_ROWTIME to false.
You can specify options for how files are named as they rotate. In setting options for rotated files' names, you can specify a prefix, suffix, and date format for the file name. You can also specify a watermark. Watermarks are drawn from a column in the source from which the file is written.
At minimum, you must specify either FILENAME_PREFIX or FILENAME_SUFFIX. All rotated files include a timestamp.
If you set ORIGINAL_FILENAME, then its value will serve as a temporary file name to use while data is being actively written.
When this file is rotated out, rotated files are named as follows:
<prefix>-<timestamp>-<watermark>-<sequenceNumber><suffix> depending on the options you specify.
If you do not set ORIGINAL_FILENAME, then the file being actively written to is given the form
Note: if you are writing from a table, and do not specify ORIGINAL_FILENAME, <date> will be the system time when the file began writing.
When this file is rotated out, rotated files are named as follows:
For example, the following options:
filename_prefix 'test-', filename_date_format 'yyyy-MM-dd_HH:mm:ss', filename_suffix '.csv', --note that you need to specify a period for filename_suffix if desired.
produce rotating file names like this:
And the following options:
filename_date_format 'yyyy-MM-dd_HH:mm:ss', filename_suffix '.csv', --note that you need to specify a period for filename_suffix if desired.
produce rotating file names like this:
You can use the ECD agent to write files to HDFS from remote locations. See Writing Data to Remote Locations for more details.
The ECD agent takes similar options, but these options need to be formatted in a properties file along the lines of the following. These properties correspond to those defined for the adapter above.
SEPARATOR=^A ROWTYPE=RECORDTYPE(INTEGER COL1, INTEGER COL2, VARCHAR(256) COL3, VARCHAR(256) COL4) SCHEMA_NAME=HADOOPWRITERTEST TABLE_NAME=HADOOPWRITERSTREAM CONFIG_PATH=/HOME/MYDIRECTORY/DEFAULT.XML AUTH_METHOD=KERBEROS AUTH_USERNAME=NN/HADOOP.DOCKER.COM@EXAMPLE.COM AUTH_KEYTAB=/TMP/NN.SERVICE.KEYTAB HDFS_OUTPUT_DIR=HDFS://STORM-S3.DISRUPTIVETECH.COM:8020/USER/SQLSTREAM/ FORMATTER=CSV QUOTE_CHARACTER= SEPARATOR=, WRITE_HEADER=FALSE DIRECTORY=/TMP ORIGINAL_FILENAME=BUS-OUTPUT.CSV FILENAME_PREFIX=OUTPUT- FILENAME_SUFFIX=.CSV FILENAME_DATE_FORMAT=YYYY-MM-DD-HH:MM:SS FILE_ROTATION_SIZE=20K' FORMATTER_INCLUDE_ROWTIME=TRUE
To invoke the agent:
From the directory $SQLSTREAM_HOME/../clienttools/EcdaAgent/ enter the following at the command line
$ ./commondataagent.sh --output --props sample.test.properties --io hdfs