DESCRIBE WAL - Kinetica Docs

Outputs the write-ahead log usage & configuration of the given tables.

DESCRIBE WAL Syntax

<DESC[RIBE]|SHOW> WAL [FOR] < [<schema name>.]<table name>[,...] | * >
[WITH OPTIONS (<option name> = '<option value>'[,...])]

The columns returned are those of the ki_wal virtual catalog table, which describes each in detail.

Only regular, persisted tables have a write-ahead log. Temporary tables, parent tables, result tables, views, logical views, and SQL procedures will return no record, so an empty result indicates that the named object has no write-ahead log—not that nothing has been written to it.

Parameters

FOR

Optional keyword for clarity

Name of the schema containing the table whose write-ahead log will be described

Name of the table whose write-ahead log will be described

Describe the write-ahead logs of all tables

Options

SHOW_SETTINGS is the only option accepted; any other will return an error.

SHOW_SETTINGS

Whether to include the SETTINGS column in the output; the default is true

Response

The response to DESCRIBE WAL is a seven-column result set, one record per table:

Output Column	Description
`SCHEMA_NAME`	Name of the schema containing the table
`TABLE_NAME`	Name of the table to which the write-ahead log belongs
`WAL_SIZE`	Number of bytes currently held in the write-ahead log, summed across the toms holding the table
`WAL_CAPACITY`	Maximum number of bytes the write-ahead log can hold, summed across the toms holding the table
`PERCENT_USED`	Percentage of the write-ahead log’s capacity currently in use
`UNCOMMITTED`	Number of bytes written to the write-ahead log that have not yet been committed to the table
`SETTINGS`	Write-ahead log configuration applied to the table, as JSON; omitted if `SHOW_SETTINGS` is `false`

WAL_SIZE, WAL_CAPACITY, PERCENT_USED & UNCOMMITTED will all be null if no part of the table reports a write-ahead log. If a size is reported but no capacity is available, WAL_SIZE & UNCOMMITTED will be populated while WAL_CAPACITY & PERCENT_USED remain null.

Examples

To describe the write-ahead log of a single table:

DESCRIBE WAL Example

DESCRIBE WAL FOR example.wal_product

DESCRIBE WAL Output

+---------------+---------------+------------+----------------+----------------------+---------------+-------------------------------------------------------------------------------------------------+
| SCHEMA_NAME   | TABLE_NAME    |   WAL_SIZE |   WAL_CAPACITY |         PERCENT_USED |   UNCOMMITTED | SETTINGS                                                                                        |
+---------------+---------------+------------+----------------+----------------------+---------------+-------------------------------------------------------------------------------------------------+
| example       | wal_product   |          0 |    10000000000 |   0.0                |             0 | {"checksum":"TRUE","max_segment_size":"500000000","segment_count":"10","sync_policy":"flush"}   |
+---------------+---------------+------------+----------------+----------------------+---------------+-------------------------------------------------------------------------------------------------+

To describe the write-ahead logs of several tables:

DESCRIBE WAL Multiple Table Example

DESCRIBE WAL FOR example.wal_product, example.wal_order

To describe the write-ahead log of a table, omitting its configuration:

DESCRIBE WAL Without Settings Example

DESCRIBE WAL FOR example.wal_product
WITH OPTIONS (SHOW_SETTINGS = 'false')

DESCRIBE WAL Without Settings Output

+---------------+---------------+------------+----------------+----------------------+---------------+
| SCHEMA_NAME   | TABLE_NAME    |   WAL_SIZE |   WAL_CAPACITY |         PERCENT_USED |   UNCOMMITTED |
+---------------+---------------+------------+----------------+----------------------+---------------+
| example       | wal_product   |          0 |    10000000000 |   0.0                |             0 |
+---------------+---------------+------------+----------------+----------------------+---------------+

​Parameters

​Options

​Response

​Examples

Parameters

Options

Response

Examples