Ldb Tool

Example data access sequence:

To dump an existing leveldb database in HEX:

To load the dumped HEX format data to a new leveldb database:

  1. $ cat /tmp/dbdump | ./ldb --db=/tmp/test_db_new load --hex --compression_type=bzip2 --block_size=65536 --create_if_missing --disable_wal

To compact an existing leveldb database:

  1. $ ./ldb --db=/tmp/test_db_new compact --compression_type=bzip2 --block_size=65536

You can specify command line --column_family=<string> for which column family your query will be against.

SST dump tool

sst_dump tool can be used to gain insights about a specific SST file. There are multiple operations that sst_dump can execute on a SST file.

  1. $ ./sst_dump
  2. file or directory must be specified.
  4. sst_dump --file=<data_dir_OR_sst_file> [--command=check|scan|raw]
  5.     --file=<data_dir_OR_sst_file>
  6.       Path to SST file or directory containing SST files
  8.     --command=check|scan|raw|verify
  9.         check: Iterate over entries in files but dont print anything except if an error is encounterd (default command)
  10.         scan: Iterate over entries in files and print them to screen
  11.         raw: Dump all the table contents to <file_name>_dump.txt
  12.         verify: Iterate all the blocks in files verifying checksum to detect possible coruption but dont print anything except if a corruption is encountered
  13.         recompress: reports the SST file size if recompressed with different
  14.                     compression types
  16.     --output_hex
  17.       Can be combined with scan command to print the keys and values in Hex
  19.     --from=<user_key>
  20.       Key to start reading from when executing check|scan
  22.     --to=<user_key>
  23.       Key to stop reading at when executing check|scan
  25.       Returns all keys with this prefix when executing check|scan
  26.       Cannot be used in conjunction with --from
  28.     --read_num=<num>
  29.       Maximum number of entries to read when executing check|scan
  31.     --verify_checksum
  32.       Verify file checksum when executing check|scan
  34.     --input_key_hex
  35.       Can be combined with --from and --to to indicate that these values are encoded in Hex
  37.     --show_properties
  38.       Print table properties after iterating over the file when executing
  39.       check|scan|raw
  41.     --set_block_size=<block_size>
  42.       Can be combined with --command=recompress to set the block size that will
  43.       be used when trying different compression algorithms
  45.     --compression_types=<comma-separated list of CompressionType members, e.g.,
  46.       kSnappyCompression>
  47.       Can be combined with --command=recompress to run recompression for this
  48.       list of compression types
  50.     --parse_internal_key=<0xKEY>
  51.       Convenience option to parse an internal key on the command line. Dumps the
  52.       internal key in hex format {'key' @ SN: type}
Dumping SST file blocks

This command will generate a txt file named /path/to/sst/000829_dump.txt. This file will contain all index blocks and data blocks encoded in Hex. It will also contain information like table properties, footer details and meta index details.

Printing entries in SST file
  1. ./sst_dump --file=/path/to/sst/000829.sst --command=scan --read_num=5

This command will print the first 5 keys in the SST file to the screen. the output may look like this

  1. 'Key1' @ 5: 1 => Value1
  2. 'Key2' @ 2: 1 => Value2
  3. 'Key3' @ 4: 1 => Value3
  4. 'Key4' @ 3: 1 => Value4

The output can be interpreted like this

Please notice that if your key has non-ascii characters, it will be hard to print it on screen, in this case it’s a good idea to use —output_hex like this

  1. ./sst_dump --file=/path/to/sst/000829.sst --command=scan --read_num=5 --output_hex

You can pass —from and —to using hexadecimal as well by using —input_key_hex

  1. ./sst_dump --file=/path/to/sst/000829.sst --command=scan --from="0x6B657932" --to="0x6B657934" --input_key_hex
Checking SST file
  1. ./sst_dump --file=/path/to/sst/000829.sst --command=check --verify_checksum

This command will Iterate over all entries in the SST file but wont print any thing except if it encountered a problem in the SST file. It will also verify the checksum.

Printing SST file properties
  1. ./sst_dump --file=/path/to/sst/000829.sst --show_properties

This command will read the SST file properties and print them, output may look like this

  1. from [] to []
  2. Process /path/to/sst/000829.sst
  3. Sst file format: block-based
  4. Table Properties:
  5. ------------------------------
  6.   # data blocks: 26541
  7.   # entries: 2283572
  8.   raw key size: 264639191
  9.   raw average key size: 115.888262
  10.   raw value size: 26378342
  11.   raw average value size: 11.551351
  12.   data block size: 67110160
  13.   index block size: 3620969
  14.   filter block size: 0
  15.   (estimated) table size: 70731129
  16.   filter policy name: N/A
  17.   # deleted keys: 571272
Trying different compression algorithms

sst_dump can be used to check the size of the file under different compression algorithms.

By using —show_compression_sizes sst_dump will recreate the SST file in memory using different compression algorithms and report the size, output may look like this

  1. from [] to []
  2. Process /path/to/sst/000829.sst
  3. Sst file format: block-based
  4. Block Size: 16384
  5. Compression: kNoCompression Size: 103974700
  6. Compression: kSnappyCompression Size: 103906223
  7. Compression: kZlibCompression Size: 80602892
  8. Compression: kBZip2Compression Size: 76250777
  9. Compression: kLZ4Compression Size: 103905572
  10. Compression: kLZ4HCCompression Size: 97234828