Introduce system variables

[apstndb]

Introduce Spanner JDBC driver style system variables.

Statements

• SHOW VARIABLE <name>;
• SET <name> = <value>;
• SHOW VARIABLES;

Flags

• --set name=value

Implemented variables

• READ_ONLY_STALENESS
• OPTIMIZER_VERSION (not work because backend bug?)
• OPTIMIZER_STATISTICS_PACKAGE
• RPC_PRIORITY
• READ_TIMESTAMP
• COMMIT_TIMESTAMP
• COMMIT_RESPONSE

Refs:

• Original proposal in spanner-cli repo: Generalize system variables cloudspannerecosystem/spanner-cli#188

Example

$ spanner-mycli -t --set 'read_only_staleness=max_staleness 10m' -v
Connected.
spanner> SHOW VARIABLES;
+------------------------------+---------------------+
| name                         | value               |
+------------------------------+---------------------+
| OPTIMIZER_STATISTICS_PACKAGE |                     |
| OPTIMIZER_VERSION            |                     |
| READ_ONLY_STALENESS          | MAX_STALENESS 10m0s |
| RPC_PRIORITY                 | MEDIUM              |
+------------------------------+---------------------+
Empty set (0.00 sec)

spanner> SELECT 1;
+-------+
|       |
| INT64 |
+-------+
| 1     |
+-------+
1 rows in set (0.14 msecs)
timestamp:            2024-10-26T22:57:45.759191+09:00
cpu time:             0.12 msecs
rows scanned:         0 rows
deleted rows scanned: 0 rows
optimizer version:    7
optimizer statistics: auto_20241023_13_33_54UTC

spanner> SET READ_ONLY_STALENESS = "READ_TIMESTAMP 2024-10-26T22:45:00+09:00";
Empty set (0.00 sec)

spanner> SELECT 1;
+-------+
|       |
| INT64 |
+-------+
| 1     |
+-------+
1 rows in set (0.2 msecs)
timestamp:            2024-10-26T22:45:00+09:00
cpu time:             0.16 msecs
rows scanned:         0 rows
deleted rows scanned: 0 rows
optimizer version:    7
optimizer statistics: auto_20241023_13_33_54UTC

spanner> SHOW VARIABLES;
+------------------------------+------------------------------------------+
| name                         | value                                    |
+------------------------------+------------------------------------------+
| OPTIMIZER_STATISTICS_PACKAGE |                                          |
| OPTIMIZER_VERSION            |                                          |
| READ_ONLY_STALENESS          | READ_TIMESTAMP 2024-10-26T22:45:00+09:00 |
| READ_TIMESTAMP               | 2024-10-26T22:45:00+09:00                |
| RPC_PRIORITY                 | MEDIUM                                   |
+------------------------------+------------------------------------------+
Empty set (0.00 sec)