Create separate metrics for BEGIN, COMMIT, and ROLLBACK statements in YSQL (#6486)

[VishnuK007]

This patch separates out the metrics for transaction begin/commit/rollback statements.

[Note: It doesn't break out PREPARE statements yet. The handling for that might require different logic, which I haven't been able to figure out yet. Might be best to separate the PREPARE handling into its own issue.]

Testing:

• I created a local YugabyteDB cluster using yb-ctl
• Used ysqlsh to create a sample table and perform of combination of begin, insert, commit, and rollback statements
• Visited the metrics page [http://127.0.0.1:13000/metrics] to ensure that these new metrics showed up and that their counters were incremented

Sample output from page shown below:

[
    {
        "type": "server",
        "id": "yb.ysqlserver",
        "metrics": [
            {
                "name": "handler_latency_yb_ysqlserver_SQLProcessor_SelectStmt",
                "count": 0,
                "sum": 0
            },
            {
                "name": "handler_latency_yb_ysqlserver_SQLProcessor_InsertStmt",
                "count": 1,
                "sum": 9579
            },
            {
                "name": "handler_latency_yb_ysqlserver_SQLProcessor_DeleteStmt",
                "count": 0,
                "sum": 0
            },
            {
                "name": "handler_latency_yb_ysqlserver_SQLProcessor_UpdateStmt",
                "count": 0,
                "sum": 0
            },
            {
                "name": "handler_latency_yb_ysqlserver_SQLProcessor_BeginStmt",
                "count": 1,
                "sum": 62
            },
            {
                "name": "handler_latency_yb_ysqlserver_SQLProcessor_CommitStmt",
                "count": 1,
                "sum": 14
            },
            {
                "name": "handler_latency_yb_ysqlserver_SQLProcessor_RollbackStmt",
                "count": 1,
                "sum": 41
            },
            {
                "name": "handler_latency_yb_ysqlserver_SQLProcessor_OtherStmts",
                "count": 0,
                "sum": 0
            },
            {
                "name": "handler_latency_yb_ysqlserver_SQLProcessor_Transactions",
                "count": 1,
                "sum": 9579
            },
            {
                "name": "handler_latency_yb_ysqlserver_SQLProcessor_AggregatePushdowns",
                "count": 0,
                "sum": 0
            }
        ]
    }
]

[CLAassistant]

All committers have signed the CLA.

[jaki]

Hi, @VishnuK007. Looks like your commits don't use your proper email, so you aren't able to sign the CLA. You should set user.email in your git config and set the same email to your GitHub account. You might also have to amend your two commits to use that email. Let me know if you need help with that. You can reach out on our community slack yugabyte-db.slack.com as well.

[VishnuK007]

Thanks @jaki. I have made the suggested changes. Can you please take a look again?

[jaki]

Thanks, @VishnuK007. I'm not too familiar with prepare. I don't see a problem with deferring it for later.

Notable issue is START TRANSACTION is regarded as OtherStmt.

[VishnuK007]

@jaki - Could you please take another look? Thanks.

[jaki]

Sorry for the long wait. Added one small comment. I'll run this through internal testing.

[jaki]

This looks good. One questionable thing is that a COMMIT on a transaction that went bad and actually rollbacks will register in metrics as a commit statement. That may or may not be desired, but I think it doesn't need to be decided in the scope of this PR.

BEGIN;
abc; -- syntax error
COMMIT; -- rollback

[jaki]

@VishnuK007

It doesn't break out PREPARE statements yet

is this outdated now? Also, I don't think we support PREPARE TRANSACTION statements anyway (issue #1125).

yugabyte=# prepare transaction 'abc';
ERROR:  PREPARE TRANSACTION not supported yet
LINE 1: prepare transaction 'abc';
        ^
HINT:  See https://github.com/YugaByte/yugabyte-db/issues/1125. Click '+' on the description to raise its priority

[kmuthukk]

This looks good. One questionable thing is that a COMMIT on a transaction that went bad and actually rollbacks will register in metrics as a commit statement. That may or may not be desired, but I think it doesn't need to be decided in the scope of this PR.

BEGIN;
abc; -- syntax error
COMMIT; -- rollback

Yes - agreed. The metric is measuring the user level operation initiated-- rather than what might happen underneath. For example, this may happen implicitly on a DML statement also if the txn conflicts with a higher priority txn.

@jaki -- assuming/when your internal test runs also pass, can you squash & merge as well.

[jaki]

I think I got it. Since "prepare" is mentioned by @kmuthukk in issue #6486, it probably means https://www.postgresql.org/docs/11/sql-prepare.html rather than https://www.postgresql.org/docs/11/sql-prepare-transaction.html.

[jaki]

And internal testing looks fine. Merging. Leaving issue #6486 open because of PREPARE statements.

[VishnuK007]

And internal testing looks fine. Merging. Leaving issue #6486 open because of PREPARE statements.

Thanks @jaki for your help!