HDFS small file merge

1.hive

Settings

There are 3 settings that should be configured before archiving is used. (Example values are shown.)

hive> set hive.archive.enabled=``true``;``hive> set hive.archive.har.parentdir.settable=``true``;``hive> set har.partfile.size=``1099511627776``;

hive.archive.enabled controls whether archiving operations are enabled.

hive.archive.har.parentdir.settable` informs Hive whether the parent directory can be set while creating the archive. In recent versions of Hadoop the option can specify the root directory of the archive. For example, if is archived with as the parent directory, then the resulting archive file will contain the directory structure . In older versions of Hadoop (prior to 2011), this option was not available and therefore Hive must be configured to accommodate this limitation.`-p``/dir1/dir2/file``/dir1``dir2/file

har.partfile.size` controls the size of the files that make up the archive. The archive will contain `/` files, rounded up. Higher values mean fewer files, but will result in longer archiving times due to the reduced number of mappers.`*size_of_partition*``har.partfile.size

Usage

Archive

Once the configuration values are set, a partition can be archived with the command:

ALTER TABLE table_name ARCHIVE PARTITION (partition_col = partition_col_value, partition_col = partiton_col_value, ...)

For example:

ALTER TABLE srcpart ARCHIVE PARTITION(ds=``'2008-04-08'``, hr=``'12'``)

Once the command is issued, a mapreduce job will perform the archiving. Unlike Hive queries, there is no output on the CLI to indicate process.

Unarchive

The partition can be reverted back to its original files with the unarchive command:

ALTER TABLE srcpart UNARCHIVE PARTITION(ds=``'2008-04-08'``, hr=``'12'``)

2.hdfs(Apache Hadoop Archives – Hadoop Archives Guide)

Overview

Hadoop archives are special format archives. A Hadoop archive maps to a file system directory. A Hadoop archive always has a .har extension. A Hadoop archive directory contains metadata (in the form of _index and _masterindex) and data (part-) files. The _index file contains the name of the files that are part of the archive and the location within the part files.

How to Create an Archive

Usage: hadoop archive -archiveName name -p <parent> [-r <replication factor>] <src>* <dest>

-archiveName is the name of the archive you would like to create. An example would be foo.har. The name should have a *.har extension. The parent argument is to specify the relative path to which the files should be archived to. Example would be :

-p /foo/bar a/b/c e/f/g

Here /foo/bar is the parent path and a/b/c, e/f/g are relative paths to parent. Note that this is a Map/Reduce job that creates the archives. You would need a map reduce cluster to run this. For a detailed example the later sections.

-r indicates the desired replication factor; if this optional argument is not specified, a replication factor of 3 will be used.

If you just want to archive a single directory /foo/bar then you can just use

hadoop archive -archiveName zoo.har -p /foo/bar -r 3 /outputdir

If you specify source files that are in an encryption zone, they will be decrypted and written into the archive. If the har file is not located in an encryption zone, then they will be stored in clear (decrypted) form. If the har file is located in an encryption zone they will stored in encrypted form.

How to Look Up Files in Archives

The archive exposes itself as a file system layer. So all the fs shell commands in the archives work but with a different URI. Also, note that archives are immutable. So, rename’s, deletes and creates return an error. URI for Hadoop Archives is

har://scheme-hostname:port/archivepath/fileinarchive

If no scheme is provided it assumes the underlying filesystem. In that case the URI would look like

har:///archivepath/fileinarchive

How to Unarchive an Archive

Since all the fs shell commands in the archives work transparently, unarchiving is just a matter of copying.

To unarchive sequentially:

hdfs dfs -cp har:///user/zoo/foo.har/dir1 hdfs:/user/zoo/newdir

To unarchive in parallel, use DistCp:

hadoop distcp har:///user/zoo/foo.har/dir1 hdfs:/user/zoo/newdir

Archives Examples

Creating an Archive

hadoop archive -archiveName foo.har -p /user/hadoop -r 3 dir1 dir2 /user/zoo

The above example is creating an archive using /user/hadoop as the relative archive directory. The directories /user/hadoop/dir1 and /user/hadoop/dir2 will be archived in the following file system directory – /user/zoo/foo.har. Archiving does not delete the input files. If you want to delete the input files after creating the archives (to reduce namespace), you will have to do it on your own. In this example, because -r 3 is specified, a replication factor of 3 will be used.

Looking Up Files

Looking up files in hadoop archives is as easy as doing an ls on the filesystem. After you have archived the directories /user/hadoop/dir1 and /user/hadoop/dir2 as in the example above, to see all the files in the archives you can just run:

hdfs dfs -ls -R har:///user/zoo/foo.har/

To understand the significance of the -p argument, lets go through the above example again. If you just do an ls (not lsr) on the hadoop archive using

hdfs dfs -ls har:///user/zoo/foo.har

The output should be:

har:///user/zoo/foo.har/dir1

har:///user/zoo/foo.har/dir2

As you can recall the archives were created with the following command

hadoop archive -archiveName foo.har -p /user/hadoop dir1 dir2 /user/zoo

If we were to change the command to:

hadoop archive -archiveName foo.har -p /user/ hadoop/dir1 hadoop/dir2 /user/zoo

then a ls on the hadoop archive using

hdfs dfs -ls har:///user/zoo/foo.har

would give you

har:///user/zoo/foo.har/hadoop/dir1

har:///user/zoo/foo.har/hadoop/dir2

Notice that the archived files have been archived relative to /user/ rather than /user/hadoop.

3.practice （demo by Internal table stored PARQUET file ）

create internal table



CREATE  TABLE xx.a(

  original_test_value DOUBLE,

  flag STRING

)

PARTITIONED BY (

  stat_date STRING,

  parametric_hash STRING

)

WITH SERDEPROPERTIES ('serialization.format'='1')

STORED AS PARQUET

LOCATION 'hdfs://nameservice1/user/hive/warehouse/xx.db/a'

copy the parquet file to new dir

sudo -u hdfs hdfs dfs -mkdir -p /user/hive/warehouse/xx.db/a/stat_date=20220125/parametric_hash=0

sudo -u hdfs hdfs dfs -cp /user/hive/warehouse/xx.db/a/stat_date=20220125/parametric_hash=0/* /user/hive/warehouse/xx.db/a/stat_date=20220125/parametric_hash=0

current hdfs file list:

Permission Owner Group Size Last Modified Replication Block Size Name
-rwxr-xr-x airflow hive 40.08 KB Feb 09 11:21 3 128 MB part-00000-e5bd2f13-a955-4920-a8ac-bd19ec031843.c000
-rwxr-xr-x airflow hive 29.07 KB Feb 09 11:21 3 128 MB part-00002-e5bd2f13-a955-4920-a8ac-bd19ec031843.c000
-rwxr-xr-x airflow hive 27.97 KB Feb 09 11:21 3 128 MB part-00003-e5bd2f13-a955-4920-a8ac-bd19ec031843.c000
-rwxr-xr-x airflow hive 27.03 KB Feb 09 11:21 3 128 MB part-00004-e5bd2f13-a955-4920-a8ac-bd19ec031843.c000
-rwxr-xr-x airflow hive 39.71 KB Feb 09 11:21 3 128 MB part-00006-e5bd2f13-a955-4920-a8ac-bd19ec031843.c000
-rwxr-xr-x airflow hive 32.54 KB Feb 09 11:21 3 128 MB part-00007-e5bd2f13-a955-4920-a8ac-bd19ec031843.c000
-rwxr-xr-x airflow hive 23.99 KB Feb 09 11:21 3 128 MB part-00011-e5bd2f13-a955-4920-a8ac-bd19ec031843.c000
-rwxr-xr-x airflow hive 23.62 KB Feb 09 11:21 3 128 MB part-00012-e5bd2f13-a955-4920-a8ac-bd19ec031843.c000
-rwxr-xr-x airflow hive 30.02 KB Feb 09 11:21 3 128 MB part-00014-e5bd2f13-a955-4920-a8ac-bd19ec031843.c000
-rwxr-xr-x airflow hive 22.91 KB Feb 09 11:21 3 128 MB part-00015-e5bd2f13-a955-4920-a8ac-bd19ec031843.c000
-rwxr-xr-x airflow hive 28.79 KB Feb 09 11:21 3 128 MB part-00016-e5bd2f13-a955-4920-a8ac-bd19ec031843.c000
-rwxr-xr-x airflow hive 19.11 KB Feb 09 11:21 3 128 MB part-00018-e5bd2f13-a955-4920-a8ac-bd19ec031843.c000

add hive partition and archive

#add partition

ALTER TABLE xx.a add  PARTITION(stat_date='20220125'parametric_hash='0') location '/user/hive/warehouse/xx.db/a/stat_date=20220125/parametric_hash=0/';

#archive

ALTER TABLE xx.a ARCHIVE PARTITION(stat_date='20220125',parametric_hash='0');

archived HDFS file list

hive merge the 12 file to 1 file as data.har

the data.har have _SUCCESS,_index,_masterindex,part-0,The actual file is stored in part-0,select the actual file by index and masterindex.
Permission Owner Group Size Last Modified Replication Block Size Name
drwxr-xr-x hdfs hive 0 B Mar 01 12:36 0 0 B data.har
Permission Owner Group Size Last Modified Replication Block Size Name
-rw-r--r-- hdfs hive 0 B Mar 01 12:36 3 128 MB _SUCCESS
-rw-r--r-- hdfs hive 3.38 KB Mar 01 12:36 3 128 MB _index
-rw-r--r-- hdfs hive 24 B Mar 01 12:36 3 128 MB _masterindex
-rw-r--r-- hdfs hive 561.31 KB Mar 01 12:36 3 512 MB part-0

effect

Positive

12 small file with 12 block merge to 1 file with 1 block.

cut down 11  metadata to offload the namenode.

nagative

#####  select * from no archive and archived table with same partition  by hiveServer2

# no archive

SELECT  * from xx.b where parametric_hash =0;

20000 行 - 93ms (+5.754s)

#archive

SELECT  * from xx.a where parametric_hash =0;

20000 行 - 102ms (+8.972s)

error: select table by impala

 select * from  xx.a;


#can not select by impala due to  Failed to connect to FS: har://hdfs-nameservice1/

SQL 错误 [500051] [HY000]: [Cloudera][ImpalaJDBCDriver](500051) ERROR processing query/statement. Error Code: 0, SQL state: Failed to connect to FS: har://hdfs-nameservice1/

Error(255): Unknown error 255

Root cause: IOException: Invalid path for the Har Filesystem. har://hdfs-nameservice1/

, Query: SELECT  `a`.`original_test_value`, `a`.`flag`, `a`.`stat_date`,`a`.`parametric_hash` FROM `xx`.`a`.

practice （demo by EXTERNAL table stored PARQUET file ）

create external table

CREATE EXTERNAL TABLE xx.b(

  original_test_value DOUBLE,

  flag STRING

)

PARTITIONED BY (

  stat_date STRING,

  parametric_hash STRING

)

WITH SERDEPROPERTIES ('serialization.format'='1')

STORED AS PARQUET

LOCATION 'hdfs://nameservice1/user/hive/warehouse/xx.db/b'

copy the parquet file to new dir

sudo -u hdfs hdfs dfs -mkdir -p /user/hive/warehouse/xx.db/b/stat_date=20220125/parametric_hash=0

sudo -u hdfs hdfs dfs -cp /user/hive/warehouse/xx.db/c/stat_date=20220125/parametric_hash=0/* /user/hive/warehouse/xx.db/b/stat_date=20220125/parametric_hash=0

current hdfs file list:

Permission Owner Group Size Last Modified Replication Block Size Name
-rwxr-xr-x airflow hive 40.08 KB Feb 09 11:21 3 128 MB part-00000-e5bd2f13-a955-4920-a8ac-bd19ec031843.c000
-rwxr-xr-x airflow hive 29.07 KB Feb 09 11:21 3 128 MB part-00002-e5bd2f13-a955-4920-a8ac-bd19ec031843.c000
-rwxr-xr-x airflow hive 27.97 KB Feb 09 11:21 3 128 MB part-00003-e5bd2f13-a955-4920-a8ac-bd19ec031843.c000
-rwxr-xr-x airflow hive 27.03 KB Feb 09 11:21 3 128 MB part-00004-e5bd2f13-a955-4920-a8ac-bd19ec031843.c000
-rwxr-xr-x airflow hive 39.71 KB Feb 09 11:21 3 128 MB part-00006-e5bd2f13-a955-4920-a8ac-bd19ec031843.c000
-rwxr-xr-x airflow hive 32.54 KB Feb 09 11:21 3 128 MB part-00007-e5bd2f13-a955-4920-a8ac-bd19ec031843.c000
-rwxr-xr-x airflow hive 23.99 KB Feb 09 11:21 3 128 MB part-00011-e5bd2f13-a955-4920-a8ac-bd19ec031843.c000
-rwxr-xr-x airflow hive 23.62 KB Feb 09 11:21 3 128 MB part-00012-e5bd2f13-a955-4920-a8ac-bd19ec031843.c000
-rwxr-xr-x airflow hive 30.02 KB Feb 09 11:21 3 128 MB part-00014-e5bd2f13-a955-4920-a8ac-bd19ec031843.c000
-rwxr-xr-x airflow hive 22.91 KB Feb 09 11:21 3 128 MB part-00015-e5bd2f13-a955-4920-a8ac-bd19ec031843.c000
-rwxr-xr-x airflow hive 28.79 KB Feb 09 11:21 3 128 MB part-00016-e5bd2f13-a955-4920-a8ac-bd19ec031843.c000
-rwxr-xr-x airflow hive 19.11 KB Feb 09 11:21 3 128 MB part-00018-e5bd2f13-a955-4920-a8ac-bd19ec031843.c000

add hive partition and archive

# add partition

ALTER TABLE xx.b add  PARTITION(stat_date='20220125',parametric_hash='0') location '/user/hive/warehouse/xx.db/b/stat_date=20220125/parametric_hash=0/';

# archive

ALTER TABLE xx.b ARCHIVE PARTITION(stat_date='20220125',parametric_hash='0');

error:

## external table don't support hive archive

ALTER TABLE xx.b ARCHIVE PARTITION(stat_date='20220125', parametric_hash='0');

FAILED: Execution Error, return code 1 from org.apache.hadoop.hive.ql.exec.DDLTask. ARCHIVE can only be performed on managed tables

## drop the partition

ALTER TABLE xx.b drop  PARTITION(stat_date='20220125' ,parametric_hash='0') ;

merge the small file with HDFS command

# bulid the har of all file in source dir output same dir

sudo -u hdfs hadoop archive -archiveName data.har -p /user/hive/warehouse/xx.db/b/stat_date=20220125/parametric_hash=0/ /user/hive/warehouse/xx.db/b/stat_date=20220125/parametric_hash=0/

# delete the original file by alreday build the har

hdfs dfs -rmr /user/hive/warehouse/xx.db/b/stat_date=20220125/parametric_hash=0/*.c000

archived HDFS file list

hive merge the 12 file to 1 file as data.har

the data.har have _SUCCESS,_index,_masterindex,part-0,The actual file is stored in part-0,select the actual file by index and masterindex.
Permission Owner Group Size Last Modified Replication Block Size Name
drwxr-xr-x hdfs hive 0 B Mar 01 12:36 0 0 B data.har
Permission Owner Group Size Last Modified Replication Block Size Name
-rw-r--r-- hdfs hive 0 B Mar 01 12:36 3 128 MB _SUCCESS
-rw-r--r-- hdfs hive 3.38 KB Mar 01 12:36 3 128 MB _index
-rw-r--r-- hdfs hive 24 B Mar 01 12:36 3 128 MB _masterindex
-rw-r--r-- hdfs hive 561.31 KB Mar 01 12:36 3 512 MB part-0

rebuild the partition

# rebuild the partition by location har file path

ALTER TABLE xx.b add  PARTITION(stat_date='20220125',parametric_hash='0') location 'har:///user/hive/warehouse/xx.db/b/stat_date=20220125/parametric_hash=0/data.har';

effect

Positive

12 small file with 12 block merge to 1 file with 1 block.

cut down 11  metadata to offload the namenode.

negative

#####  select * from no archive and archived table with same partition  by hiveServer2

# no archive

SELECT  * from xx.b where parametric_hash =0;

20000 行 - 93ms (+5.754s)

#archive

SELECT  * from xx.b where parametric_hash =0;

20000 行 - 102ms (+8.972s)

error: select table by impala

select * from  xx.b;


#can not select by impala due to  Failed to connect to FS: har://hdfs-nameservice1/

SQL 错误 [500312] [HY000]: [Cloudera][ImpalaJDBCDriver](500312) Error in fetching data rows: Disk I/O error on impala03-dev:22000: Failed to open HDFS file har:/user/hive/warehouse/xx.db/b/stat_date=20220125/parametric_hash=0/data.har/part-00006-e5bd2f13-a955-4920-a8ac-bd19ec031843.c000

Error(22): Invalid argument

Root cause: IllegalArgumentException: Wrong FS: har:/user/hive/warehouse/xx.db/b/stat_date=20220125/parametric_hash=0/data.har/part-00006-e5bd2f13-a955-4920-a8ac-bd19ec031843.c000, expected: hdfs://nameservice1

[Not achieved]how to fix the problem by select the archived table by impala

1.designate the HDFS HA name service when location the HAR file into partition

drop the partition location by har://path

ALTER TABLE xx.b drop  PARTITION(stat_date='20220125',parametric_hash='0') ;

Dropped the partition stat_date=20220125/parametric_hash=0

add the new partition location by hdfs://nameservice/path

ALTER TABLE xx.b add  PARTITION(stat_date='20220125',parametric_hash='0') location 'hdfs://nameservice1/user/hive/warehouse/xx.db/b/stat_date=20220125/parametric_hash=0/data.har';

failed : select from the new partition

Failed with exception java.io.IOException:org.apache.parquet.io.ParquetDecodingException: Can not read value at 0 in block -1 in file hdfs://nameservice1/user/hive/warehouse/xx.db/b/stat_date=20220125/parametric_hash=0/data.har/part-0

2.designate the HDFS namenode:port when location the HAR file into partition

drop the partition location by hdfs://nameservice/path

ALTER TABLE xx.b drop  PARTITION(stat_date='20220125',parametric_hash='0') ;

Dropped the partition stat_date=20220125/parametric_hash=0

add the new partition location by hdfs://namenode:port/path

 ALTER TABLE xx.b add  PARTITION(stat_date='20220125',parametric_hash='0') location 'hdfs://192.168.1.170:8020/user/hive/warehouse/xx.db/b/stat_date=20220125/parametric_hash=0/data.har';

OK

Time taken: 0.088 seconds

failed : select from the new partition

hive> select * from xx.b limit 10;

OK

Failed with exception java.io.IOException:org.apache.parquet.io.ParquetDecodingException: Can not read value at 0 in block -1 in file hdfs://192.168.1.170:8020/user/hive/warehouse/xx.db/b/stat_date=20220125/parametric_hash=0/data.har/part-0

3.designate the har://nameservice/path when location the HAR file into partition

drop the partition location by hdfs://path

ALTER TABLE xx.b drop  PARTITION(stat_date='20220125',parametric_hash='0') ;

Dropped the partition stat_date=20220125/parametric_hash=0

add the new partition location by har://nameservice/path

ALTER TABLE xx.b add  PARTITION(stat_date='20220125',parametric_hash='0') location 'har://hdfs-nameservice1/user/hive/warehouse/xx.db/b/stat_date=20220125/parametric_hash=0/data.har';

success hive : select from the new partition

select * from xx.b limit 10;

Time taken: 1.056 seconds, Fetched: 10 row(s)

failed impala : select from the new partition

SQL 错误 [500051] [HY000]: [Cloudera][ImpalaJDBCDriver](500051) ERROR processing query/statement. Error Code: 0, SQL state: Failed to connect to FS: har://hdfs-nameservice1/

Error(255): Unknown error 255

Root cause: IOException: Invalid path for the Har Filesystem. har://hdfs-nameservice1/

, Query: SELECT `b`.`original_test_value`, `b`.`flag` `b`.`stat_date`,  `b`.`parametric_hash` FROM `test_xac_dws`.`b` LIMIT 10.

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