TRACING

Enables or disables tracing for all CQL statements in the current CQLSH session. Tracing can show tracing input from any or all nodes in the cluster. Use tracing to troubleshoot performance problems. Detailed transaction information related to internal operations is captured in the system_traces keyspace.

To enable or disable tracing for the entire cluster, run nodetool settraceprobability for each node. For information about probabilistic tracing, see nodetool settraceprobability.

When a query runs in a tracing session, a session ID is shown in the query results. In addition, an entry with the high-level details such as session ID, client, and session length, is written to the system_traces.session table. Details for each operation are written to the system_traces.events table.

The session ID is used by the SHOW SESSION tracing_session_id command to display detailed event information.

Tracing information is saved for 24 hours. To save tracing data for longer than 24 hours, copy the data to another location.

Synopsis

TRACING [ ON | OFF ]
Syntax legend
Legend
Syntax conventions Description

UPPERCASE

Literal keyword.

Lowercase

Not literal.

< >

Variable value. Replace with a user-defined value.

[]

Optional. Square brackets ([]) surround optional command arguments. Do not type the square brackets.

( )

Group. Parentheses ( ( ) ) identify a group to choose from. Do not type the parentheses.

|

Or. A vertical bar (|) separates alternative elements. Type any one of the elements. Do not type the vertical bar.

...

Repeatable. An ellipsis ( ... ) indicates that you can repeat the syntax element as often as required.

'<Literal string>'

Single quotation (') marks must surround literal strings in CQL statements. Use single quotation marks to preserve upper case.

{ <key> : <value> }

Map collection. Braces ({ }) enclose map collections or key value pairs. A colon separates the key and the value.

<datatype2

Set, list, map, or tuple. Angle brackets ( < > ) enclose data types in a set, list, map, or tuple. Separate the data types with a comma.

<cql_statement>;

End CQL statement. A semicolon (;) terminates all CQL statements.

[--]

Separate the command line options from the command arguments with two hyphens ( -- ). This syntax is useful when arguments might be mistaken for command line options.

' <<schema\> ... </schema\>> '

Search CQL only: Single quotation marks (') surround an entire XML schema declaration.

@<xml_entity>='<xml_entity_type>'

Search CQL only: Identify the entity and literal value to overwrite the XML element in the schema and solrConfig files.

ON

Enables tracing.

OFF

Disables tracing.

Examples

Tracing a write request

The following example shows tracing activity on a three node cluster. The cluster has a keyspace that has a replication factor of three, and an employee table similar to the table in Using a compound primary key.

The tracing shows that the coordinator performs these actions:

  • Identifies the target nodes for replication of the row.

  • Writes the row to the commit log and memtable.

  • Confirms completion of the request.

Turn on tracing:

TRACING ON

Insert a record into the cyclist_name table:

INSERT INTO cycling.cyclist_name (
  id,
  lastname,
  firstname
) VALUES (
  e7ae5cf3-d358-4d99-b900-85902fda9bb0,
  'FRAME',
  'Alex'
);

The request and each step are captured and displayed:

Tracing session: 9b378c70-b114-11e6-89b5-b7fad52e1885

 activity                                                                                         | timestamp                  | source    | source_elapsed | client
------------------------------------------------------------------------------------------------------------------------------------------------------------------------
                                                                               Execute CQL3 query | 2016-11-22 16:34:34.300000 | 127.0.0.1 |              0 | 127.0.0.1
 Parsing INSERT INTO cycling.cyclist_name (id, lastname, firstname)
 VALUES (e7ae5cf3-d358-4d99-b900-85902fda9bb0, 'FRAME','Alex'); [Native-Transport-Requests-1]     | 2016-11-22 16:34:34.305000 | 127.0.0.1 |           5935 | 127.0.0.1
                                                Preparing statement [Native-Transport-Requests-1] | 2016-11-22 16:34:34.308000 | 127.0.0.1 |           9199 | 127.0.0.1
                                  Determining replicas for mutation [Native-Transport-Requests-1] | 2016-11-22 16:34:34.330000 | 127.0.0.1 |          30530 | 127.0.0.1
                                                         Appending to commitlog [MutationStage-3] | 2016-11-22 16:34:34.330000 | 127.0.0.1 |          30979 | 127.0.0.1
                                                Adding to cyclist_name memtable [MutationStage-3] | 2016-11-22 16:34:34.330000 | 127.0.0.1 |          31510 | 127.0.0.1
                                                                                 Request complete | 2016-11-22 16:34:34.333633 | 127.0.0.1 |          33633 | 127.0.0.1

The source_elapsed column value is the elapsed time of the event on the source node in microseconds.

Tracing a sequential scan

A single row is spread across multiple SSTables. Reading one row involves reading data from multiple SSTables, as shown by the trace for this request to read rows from the cyclist_name table:

SELECT *
FROM cycling.cyclist_name;

The query results display first, followed by the session ID and session details:

 id                                   | firstname | lastname
--------------------------------------+-----------+-----------------
 e7ae5cf3-d358-4d99-b900-85902fda9bb0 |      Alex |           FRAME
 fb372533-eb95-4bb4-8685-6ef61e994caa |   Michael |        MATTHEWS
 5b6962dd-3f90-4c93-8f61-eabfa4a803e2 |  Marianne |             VOS
 220844bf-4860-49d6-9a4b-6b5d3a79cbfb |     Paolo |       TIRALONGO
 6ab09bec-e68e-48d9-a5f8-97e6fb4c9b47 |    Steven |      KRUIKSWIJK
 e7cd5752-bc0d-4157-a80f-7523add8dbcd |      Anna | VAN DER BREGGEN

(6 rows)

Tracing session: 117c1440-b116-11e6-89b5-b7fad52e1885

 activity                                                                                                                      | timestamp                  | source    | source_elapsed | client
-------------------------------------------------------------------------------------------------------------------------------+----------------------------+-----------+----------------+-----------
                                                                                                            Execute CQL3 query | 2016-11-22 16:45:02.212000 | 127.0.0.1 |              0 | 127.0.0.1
                                                    Parsing SELECT * FROM cycling.cyclist_name ; [Native-Transport-Requests-1] | 2016-11-22 16:45:02.212000 | 127.0.0.1 |            372 | 127.0.0.1
                                                                             Preparing statement [Native-Transport-Requests-1] | 2016-11-22 16:45:02.212000 | 127.0.0.1 |            541 | 127.0.0.1
                                                                       Computing ranges to query [Native-Transport-Requests-1] | 2016-11-22 16:45:02.213000 | 127.0.0.1 |            807 | 127.0.0.1
 Submitting range requests on 257 ranges with a concurrency of 257 (0.3 rows per range expected) [Native-Transport-Requests-1] | 2016-11-22 16:45:02.213000 | 127.0.0.1 |           1632 | 127.0.0.1
                                                           Submitted 1 concurrent range requests [Native-Transport-Requests-1] | 2016-11-22 16:45:02.215000 | 127.0.0.1 |           3002 | 127.0.0.1
                 Executing seq scan across 1 sstables for (min(-9223372036854775808), min(-9223372036854775808)] [ReadStage-2] | 2016-11-22 16:45:02.215000 | 127.0.0.1 |           3130 | 127.0.0.1
                                                                               Read 6 live and 0 tombstone cells [ReadStage-2] | 2016-11-22 16:45:02.216000 | 127.0.0.1 |           3928 | 127.0.0.1
                                                                                                              Request complete | 2016-11-22 16:45:02.216252 | 127.0.0.1 |           4252 | 127.0.0.1

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