HDFS

Name

hdfs

Description

HDFS table-valued-function(tvf), allows users to read and access file contents on S3-compatible object storage, just like accessing relational table. Currently supports csv/csv_with_names/csv_with_names_and_types/json/parquet/orc file format.

syntax

hdfs(
  "uri" = "..",
  "fs.defaultFS" = "...",
  "hadoop.username" = "...",
  "format" = "csv",
  "keyn" = "valuen" 
  ...
  );

parameter description

Related parameters for accessing hdfs:

uri: (required) hdfs uri. If the uri path does not exist or the files are empty files, hdfs tvf will return an empty result set.
fs.defaultFS: (required)
hadoop.username: (required) Can be any string, but cannot be empty.
hadoop.security.authentication: (optional)
hadoop.username: (optional)
hadoop.kerberos.principal: (optional)
hadoop.kerberos.keytab: (optional)
dfs.client.read.shortcircuit: (optional)
dfs.domain.socket.path: (optional)

Related parameters for accessing HDFS in HA mode:

dfs.nameservices: (optional)
dfs.ha.namenodes.your-nameservices: (optional)
dfs.namenode.rpc-address.your-nameservices.your-namenode: (optional)
dfs.client.failover.proxy.provider.your-nameservices: (optional)

File format parameters:

format: (required) Currently support csv/csv_with_names/csv_with_names_and_types/json/parquet/orc/avro
column_separator: (optional) default \t.
line_delimiter: (optional) default \n.
compress_type: (optional) Currently support UNKNOWN/PLAIN/GZ/LZO/BZ2/LZ4FRAME/DEFLATE/SNAPPYBLOCK. Default value is UNKNOWN, it will automatically infer the type based on the suffix of uri.
The following 6 parameters are used for loading in json format. For specific usage methods, please refer to: Json Load
read_json_by_line: (optional) default "true"
strip_outer_array: (optional) default "false"
json_root: (optional) default ""
json_paths: (optional) default ""
num_as_string: (optional) default false
fuzzy_parse: (optional) default false
SinceVersion devThe following 2 parameters are used for loading in csv format
trim_double_quotes: Boolean type (optional), the default value is false. True means that the outermost double quotes of each field in the csv file are trimmed.
skip_lines: Integer type (optional), the default value is 0. It will skip some lines in the head of csv file. It will be disabled when the format is csv_with_names or csv_with_names_and_types.

other kinds of parameters:

path_partition_keys: (optional) Specifies the column names carried in the file path. For example, if the file path is /path/to/city=beijing/date="2023-07-09", you should fill in path_partition_keys="city,date". It will automatically read the corresponding column names and values from the path during load process.
resource：（optional）Specify the resource name. Hdfs Tvf can use the existing Hdfs resource to directly access Hdfs. You can refer to the method for creating an Hdfs resource: CREATE-RESOURCE. This property is supported starting from version 2.1.4 .

Tip

To directly query a TVF or create a VIEW based on that TVF, you need to have usage permission for that resource. To query a VIEW created based on TVF, you only need select permission for that VIEW.

Examples

Read and access csv format files on hdfs storage.

MySQL [(none)]> select * from hdfs(
            "uri" = "hdfs://127.0.0.1:842/user/doris/csv_format_test/student.csv",
            "fs.defaultFS" = "hdfs://127.0.0.1:8424",
            "hadoop.username" = "doris",
            "format" = "csv");
+------+---------+------+
| c1   | c2      | c3   |
+------+---------+------+
| 1    | alice   | 18   |
| 2    | bob     | 20   |
| 3    | jack    | 24   |
| 4    | jackson | 19   |
| 5    | liming  | 18   |
+------+---------+------+

Read and access csv format files on hdfs storage in HA mode.

MySQL [(none)]> select * from hdfs(
            "uri" = "hdfs://127.0.0.1:842/user/doris/csv_format_test/student.csv",
            "fs.defaultFS" = "hdfs://127.0.0.1:8424",
            "hadoop.username" = "doris",
            "format" = "csv",
            "dfs.nameservices" = "my_hdfs",
            "dfs.ha.namenodes.my_hdfs" = "nn1,nn2",
            "dfs.namenode.rpc-address.my_hdfs.nn1" = "nanmenode01:8020",
            "dfs.namenode.rpc-address.my_hdfs.nn2" = "nanmenode02:8020",
            "dfs.client.failover.proxy.provider.my_hdfs" = "org.apache.hadoop.hdfs.server.namenode.ha.ConfiguredFailoverProxyProvider");
+------+---------+------+
| c1   | c2      | c3   |
+------+---------+------+
| 1    | alice   | 18   |
| 2    | bob     | 20   |
| 3    | jack    | 24   |
| 4    | jackson | 19   |
| 5    | liming  | 18   |
+------+---------+------+

Can be used with desc function :

MySQL [(none)]> desc function hdfs(
            "uri" = "hdfs://127.0.0.1:8424/user/doris/csv_format_test/student_with_names.csv",
            "fs.defaultFS" = "hdfs://127.0.0.1:8424",
            "hadoop.username" = "doris",
            "format" = "csv_with_names");

Keywords

hdfs, table-valued-function, tvf

Best Practice

For more detailed usage of HDFS tvf, please refer to S3 tvf, The only difference between them is the way of accessing the storage system.

HDFS​

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