system.merges
-------------
Contains information about merges currently in process for tables in the MergeTree family.

Columns:
::
  database String                    - Name of the database the table is located in.
  table String                       - Name of the table.
  elapsed Float64                    - Time in seconds since the merge started.
  progress Float64                   - Percent of progress made, from 0 to 1.
  num_parts UInt64                   - Number of parts to merge.
  result_part_name String            - Name of the part that will be formed as the result of the merge.
  total_size_bytes_compressed UInt64 - Total size of compressed data in the parts being merged.
  total_size_marks UInt64            - Total number of marks in the parts being merged.
  bytes_read_uncompressed UInt64     - Amount of bytes read, decompressed.
  rows_read UInt64                   - Number of rows read.
  bytes_written_uncompressed UInt64  - Amount of bytes written, uncompressed.
  rows_written UInt64                - Number of rows written.