add index to pop_basis for pop tx queries

[ClaytonNorthey92]

add index to pop_basis so we can avoid "rescans" in the query

Summary
rescans were taking a long time in the pop tx query, add an index to avoid them.

Changes

Note: I call my index clayton_tmp_0 for testing purposes, I have removed this indexed and renamed it in the PR.

before (for about 6-7k rows matching the pop_basis query)

 Limit  (cost=26902.86..26903.11 rows=100 width=1321) (actual time=1979.313..1979.328 rows=100 loops=1)
   InitPlan 1 (returns $0)
     ->  Limit  (cost=8.69..8.86 rows=1 width=41) (actual time=0.084..0.085 rows=1 loops=1)
           ->  Index Scan Backward using l2_keystone_l2_block_number_idx on l2_keystones  (cost=0.28..1175.82 rows=6989 width=41) (actual time=0.044..0.083 rows=51 loops=1)
   ->  Sort  (cost=26894.00..26911.03 rows=6811 width=1321) (actual time=1979.312..1979.319 rows=100 loops=1)
         Sort Key: pop_basis.id
         Sort Method: top-N heapsort  Memory: 282kB
         ->  Bitmap Heap Scan on pop_basis  (cost=89.35..26633.69 rows=6811 width=1321) (actual time=4.331..1974.378 rows=13371 loops=1)
               Recheck Cond: (l2_keystone_abrev_hash = $0)
               Filter: (btc_block_hash IS NOT NULL)
               Heap Blocks: exact=6438
               ->  Bitmap Index Scan on l2_keystone_abrev_hash_idx  (cost=0.00..87.64 rows=6811 width=0) (actual time=3.113..3.113 rows=13371 loops=1)
                     Index Cond: (l2_keystone_abrev_hash = $0)
 Planning Time: 0.604 ms
 Execution Time: 1979.356 ms

after (for a similar number of pop_basis rows)

 Limit  (cost=11.95..416.75 rows=100 width=1321) (actual time=0.928..5.350 rows=100 loops=1)
   InitPlan 1 (returns $0)
     ->  Limit  (cost=11.22..11.38 rows=1 width=41) (actual time=0.264..0.264 rows=1 loops=1)
           ->  Index Scan Backward using l2_keystone_l2_block_number_idx on l2_keystones  (cost=0.28..1175.82 rows=6989 width=41) (actual time=0.013..0.261 rows=66 loops=1)
   ->  Index Scan using clayton_tmp_0 on pop_basis  (cost=0.56..27656.70 rows=6832 width=1321) (actual time=0.928..5.319 rows=100 loops=1)
         Index Cond: (l2_keystone_abrev_hash = $0)
 Planning Time: 0.206 ms
 Execution Time: 5.375 ms
(8 rows)

[jcvernaleo]

OK