Use spanner-cli specific request tags for queries like `SELECT 1`

[takabow]

spanner-cli itself may issue SQLs in addition to SQLs directly issued by users.
For example, SELECT 1 issued for heartbeat purposes, etc.

Such queries appear in Cloud Spanner's query statistics and may confuse users who are unaware that spanner-cli is issuing them.
To identify such queries more easily, I suggest adding spanner-cli specific request tags to the queries.

As far as I can find, spanner-cli seems to issue its own SELECT query for the following uses.

• SELECT 1 - At the beginning of a Read-write transaction
• SELECT 1 - To check if DB exists.
• SELECT 1 - Heartbeat
• SELECT ... FROM INFORMATION_SCHEMA.TABLES ... - SHOW TABLES
• SELECT ... FROM INFORMATION_SCHEMA.INDEXES ... - SHOW INDEX
• SELECT ... FROM INFORMATION_SCHEMA.COLUMNS ... - SHOW COLUMNS

I am not sure what specific string of text to tag, so I need your opinion.

As an example, it seems that Cloud Console uses sys_cloud_console_* to issue some queries.

spanner> SELECT SUBSTR(text,0,20) AS text, request_tag,
      -> FROM spanner_sys.query_stats_top_minute
      -> WHERE request_tag <> "";
+----------------------+---------------------------------------------+
| text                 | request_tag                                 |
+----------------------+---------------------------------------------+
| SELECT TABLE_NAME, T | sys_cloud_console_DatabaseTables            |
| SELECT VIEW_DEFINITI | sys_cloud_console_TableDetailViewDefinition |
| SELECT OPTION_NAME,  | sys_cloud_console_DatabaseOptions           |
| SELECT INDEX_NAME, I | sys_cloud_console_TableDetailIndexes        |
| SELECT TABLE_NAME, C | sys_cloud_console_TableDetailTableColumnMap |
| SELECT TABLE_NAME, C | sys_cloud_console_DatabaseTableColumnMap    |
| SELECT TABLE_NAME, C | sys_cloud_console_TableDetailColumns        |
| SELECT TABLE_NAME, T | sys_cloud_console_TableDetail               |
| SELECT TABLE_NAME, T | sys_cloud_console_DatabaseTables            |
| SELECT OPTION_NAME,  | sys_cloud_console_DatabaseOptions           |
| SELECT TABLE_NAME, C | sys_cloud_console_DatabaseTableColumnMap    |
+----------------------+---------------------------------------------+

[takabow]

One idea is to use spanner-cli_*, such as spanner-cli_heartbeat

[takabow]

like the following.

+----------------------------+---------------------------------------------+
| request_tag idea           | When is the query issued?                   |
+----------------------------+---------------------------------------------+
| spanner-cli_BeginRW        | BEGIN RW - `SELECT 1`                       |
| spanner-cli_DatabaseExists | DatabaseExists - `SELECT 1`                 |
| spanner-cli_Heartbeat      | Heartbeat - `SELECT 1`                      |
| spanner-cli_ShowTables     | SHOW TABLES - `INFORMATION_SCHEMA.TABLES`   |
| spanner-cli_ShowIndex      | SHOW INDEX - `INFORMATION_SCHEMA.INDEXES`   |
| spanner-cli_ShowColmuns    | SHOW COLUMNS - `INFORMATION_SCHEMA.COLUMNS` |
+----------------------------+---------------------------------------------+

[yfuruyama]

@takabow Looks good! Thanks for raising this.

One thing I want to discuss is whether we should use different tags for different use cases.

If we use the same tag like spanner-cli for all use cases, it's easier for us to maintain the code and also it would be easier/intuitive for users to exclude the spaner-cli requests: WHERE request_tag != "spanner-cli".

Do we think it's better to use different tags for each use case?

[apstndb]

The request tag is effectively used as the key of the query stats entry, not part of the compound key.

TEXT
Statistics for multiple queries that have the same tag string are grouped in a single row with the REQUEST_TAG matching that tag string. Only the text of one of those queries is shown in this field, truncated to approximately 64KB.

TEXT_FINGERPRINT
The hash of the REQUEST_TAG value if present; Otherwise, the hash of the TEXT value.

I think this behavior is confusing and it is better to use different request_tag for each query to ease troubleshooting.

it would be easier/intuitive for users to exclude the spaner-cli requests: WHERE request_tag != "spanner-cli".

I think it is not hard to use WHERE request_tag NOT LIKE "spanner-cli_%".

[yfuruyama]

Ah I didn't know that the multiple requests with the same tag are grouped into the single row of query statistics regardless of the actual queries. Then using the same tag doesn't make sense from semantics perspective.

[takabow]

As apstndb suggested, I would like to implement this with individual tags.

[yfuruyama]

Sounds good to me!