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ClickHouse/docs/en/operations/system-tables/tables.md
Azat Khuzhin 32a45d0dee Implement lifetime_rows/lifetime_bytes for Buffer engine 
Buffer engine is usually used on INSERTs, but right now there is no way
to track number of INSERTed rows per-table, since only summary metrics
exists:
- StorageBufferRows
- StorageBufferBytes

But it can be pretty useful to track INSERTed rows rate (and it can be
exposed via http_handlers for i.e. prometheus)
2020-07-11 16:06:11 +03:00

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system.tables

Contains metadata of each table that the server knows about. Detached tables are not shown in system.tables.

This table contains the following columns (the column type is shown in brackets):

  • database (String) — The name of the database the table is in.

  • name (String) — Table name.

  • engine (String) — Table engine name (without parameters).

  • is_temporary (UInt8) - Flag that indicates whether the table is temporary.

  • data_path (String) - Path to the table data in the file system.

  • metadata_path (String) - Path to the table metadata in the file system.

  • metadata_modification_time (DateTime) - Time of latest modification of the table metadata.

  • dependencies_database (Array(String)) - Database dependencies.

  • dependencies_table (Array(String)) - Table dependencies (MaterializedView tables based on the current table).

  • create_table_query (String) - The query that was used to create the table.

  • engine_full (String) - Parameters of the table engine.

  • partition_key (String) - The partition key expression specified in the table.

  • sorting_key (String) - The sorting key expression specified in the table.

  • primary_key (String) - The primary key expression specified in the table.

  • sampling_key (String) - The sampling key expression specified in the table.

  • storage_policy (String) - The storage policy:

  • total_rows (Nullable(UInt64)) - Total number of rows, if it is possible to quickly determine exact number of rows in the table, otherwise Null (including underying Buffer table).

  • total_bytes (Nullable(UInt64)) - Total number of bytes, if it is possible to quickly determine exact number of bytes for the table on storage, otherwise Null (does not includes any underlying storage).

    • If the table stores data on disk, returns used space on disk (i.e. compressed).
    • If the table stores data in memory, returns approximated number of used bytes in memory.

  • lifetime_rows (Nullable(UInt64)) - Total number of rows INSERTed since server start (only for Buffer tables).

  • lifetime_bytes (Nullable(UInt64)) - Total number of bytes INSERTed since server start (only for Buffer tables).

The system.tables table is used in SHOW TABLES query implementation.