docs/deleteKeyValuePair.md

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# Apache Accumulo Key-Value Pair Removal Example

This example shows how Accumulo internals handle removing a key-value pair

```
$ /path/to/accumulo shell -u username -p secret
username@instance> createnamespace examples
username@instance> createtable examples.deleteKeyValuePair
username@instance examples.deleteKeyValuePair> insert 567890 name first Joe
username@instance examples.deleteKeyValuePair> insert 567890 name last Smith
username@instance examples.deleteKeyValuePair> insert 567890 address city Columbia
```

```
username@instance examples.deleteKeyValuePair> scan
567890 address:city []    Columbia
567890 name:first []    Joe
567890 name:last []    Smith
```

```
username@instance examples.deleteKeyValuePair> flush -w
2019-04-18 11:01:47,444 [shell.Shell] INFO : Flush of table deleteKeyValuePair completed.
```

Get the examples.deleteKeyValuePair table id.

```
username@instance examples.deleteKeyValuePair> tables -l
accumulo.metadata    =>        !0
accumulo.replication =>      +rep
accumulo.root        =>        +r
deleteKeyValuePair   =>        1t
```

Scan accumulo.metadata table to see the list of RFiles Accumulo is currently using.

```
username@instance examples.deleteKeyValuePair> scan -t accumulo.metadata -c file -r 1t<
1t< file:hdfs://localhost:8020/accumulo/tables/1t/default_tablet/F00007em.rf
```

View the contents of RFile and verify each key-value pair's deletion flag is false.

```
$ /path/to/accumulo rfile-info -d hdfs://localhost/accumulo/tables/1t/default_tablet/F00007em.rf
RFile Version            : 8

Locality group           : <DEFAULT>
    Num   blocks           : 1
    Index level 0          : 37 bytes  1 blocks
    First key              : 567890 address:city [] 1555418057811 false
    Last key               : 567890 name:last [] 1555418063052 false
    Num entries            : 3
    Column families        : [address, name]

Meta block     : BCFile.index
      Raw size             : 4 bytes
      Compressed size      : 12 bytes
      Compression type     : gz

Meta block     : RFile.index
      Raw size             : 141 bytes
      Compressed size      : 97 bytes
      Compression type     : gz
      
567890 address:city [] 1618581304723 false -> Columbia
567890 name:first [] 1618581291527 false -> Joe
567890 name:last [] 1618581297272 false -> Smith
```
Delete a key-value pair and view a newly created RFile to verify the deletion flag is true.

```
$ /path/to/accumulo shell -u username -p secret
username@instance> table examples.deleteKeyValuePair
username@instance examples.deleteKeyValuePair> delete 567890 name first
username@instance examples.deleteKeyValuePair> flush -w
```

```
username@instance examples.deleteKeyValuePair> scan -t accumulo.metadata -c file -r 1t<
1t< file:hdfs://localhost:8020/accumulo/tables/1t/default_tablet/F00007em.rf
1t< file:hdfs://localhost:8020/accumulo/tables/1t/default_tablet/F00007fq.rf
```

```
$ /path/to/accumulo rfile-info -d hdfs://localhost/accumulo/tables/1t/default_tablet/F00007fq.rf
RFile Version            : 8

Locality group           : <DEFAULT>
    Num   blocks           : 1
    Index level 0          : 38 bytes  1 blocks
    First key              : 567890 name:first [] 1555419184531 true
    Last key               : 567890 name:first [] 1555419184531 true
    Num entries            : 1
    Column families        : [name]

Meta block     : BCFile.index
      Raw size             : 4 bytes
      Compressed size      : 12 bytes
      Compression type     : gz

Meta block     : RFile.index
      Raw size             : 121 bytes
      Compressed size      : 68 bytes
      Compression type     : gz
      
567890 name:first [] 1618581499491 true ->
```

Compact the RFiles and verify the key-value pair was removed.  The new RFile will start with 'A'.

```
$ /path/to/accumulo shell -u username -p secret
username@instance> compact -t examples.deleteKeyValuePair -w
2019-04-17 08:17:15,468 [shell.Shell] INFO : Compacting table ...
2019-04-17 08:17:16,143 [shell.Shell] INFO : Compaction of table examples.deleteKeyValuePair 
completed for given range
```

```
username@instance> scan -t accumulo.metadata -c file -r 1t<
lt< file:hdfs://localhost:8020/accumulo/tables/1t/default_tablet/A00007g1.rf
```

 ```
$ /path/to/accumulo rfile-info -v hdfs://localhost/accumulo/tables/1t/default_tablet/A00007g1.rf
RFile Version            : 8

Locality group           : <DEFAULT>
    Num   blocks           : 1
    Index level 0          : 37 bytes  1 blocks
    First key              : 567890 address:city [] 1555418057811 false
    Last key               : 567890 name:last [] 1555418063052 false
    Num entries            : 2
    Column families        : [address, name]

Meta block     : BCFile.index
      Raw size             : 4 bytes
      Compressed size      : 12 bytes
      Compression type     : gz

Meta block     : RFile.index
      Raw size             : 141 bytes
      Compressed size      : 96 bytes
      Compression type     : gz
      
Locality Group: <DEFAULT>
Visibility                 Number of keys          Percent of keys      Number of blocks        Percent of blocks
                                2                       100.00%                 1                  100.00%
Number of keys: 2
     
```