Modify outer left join query to use existing index.

[winder]

Summary

Modify outer left join query to use existing index.

Test Plan

Manual performance testing and EXPLAIN analysis.

[tolikzinovyev]

what happens when t.extra->>'root-intra' is empty string?

[winder]

what happens when t.extra->>'root-intra' is empty string?

That case is why the query needs to be left outer join instead of a simple join. When nothing has matched for the root transaction, the rest of the result is still returned.

Here is a test query to demonstrate:

select
	root.txid root_txid,
	t.extra,
	t.intra,
	t.round
from
	txn t
join block_header h on
	t.round = h.round
left outer join txn root on
	t.round = root.round
	and (t.extra->>'root-intra')::int = root.intra
where
	t.round = 18461108

root_txid                                           |extra                                                                                   |intra|round   |
----------------------------------------------------+----------------------------------------------------------------------------------------+-----+--------+
                                                    |{}                                                                                      |    0|18461108|
                                                    |{}                                                                                      |    1|18461108|
                                                    |{}                                                                                      |    2|18461108|
                                                    |{}                                                                                      |    3|18461108|
                                                    |{}                                                                                      |    4|18461108|
                                                    |{}                                                                                      |    5|18461108|
                                                    |{}                                                                                      |    6|18461108|
                                                    |{}                                                                                      |    7|18461108|
5DVVQAULIA4RBYPBUNAPTCBNQXUFXBR6SGZ4NHV7XTF77LMTUTNQ|{"root-txid": "5DVVQAULIA4RBYPBUNAPTCBNQXUFXBR6SGZ4NHV7XTF77LMTUTNQ", "root-intra": "7"}|    8|18461108|
5DVVQAULIA4RBYPBUNAPTCBNQXUFXBR6SGZ4NHV7XTF77LMTUTNQ|{"root-txid": "5DVVQAULIA4RBYPBUNAPTCBNQXUFXBR6SGZ4NHV7XTF77LMTUTNQ", "root-intra": "7"}|    9|18461108|
                                                    |{}                                                                                      |   10|18461108|
                                                    |{}                                                                                      |   11|18461108|
                                                    |{}                                                                                      |   12|18461108|

[tolikzinovyev]

Assuming there is a unit test, LGTM!