Speedup of blocks_without_reward_query

[vbaranov]

Motivation

The query https://github.com/poanetwork/blockscout/blob/8c62be450d9a78b4a52ae6c3900f6b383d2b8382/apps/explorer/lib/explorer/chain/block.ex#L118 executes more than 5 hours on ETH Mainnet instance.

This PR aims to decrease the execution time.

Changelog

1. Add partial index on block_rewards table block_hash column where address type is validator
2. Decrease subsets of tables before joins, not after.

Before the changes:

8740 | 05:36:11.251542 |SELECT b0."hash", b0."consensus", b0."difficulty", b0."gas_limit", b0."gas_used", b0."nonce", b0."number", b0."size", b0."timestamp", b0."total_difficulty", b0."internal_transactions_indexed_at", b0."refetch_needed", b0."inserted_at", b0."updated_at", b0."miner_hash", b0."parent_hash" FROM "blocks" AS b0 LEFT OUTER JOIN "block_rewards" AS b1 ON b1."block_hash" = b0."hash" WHERE (b1."block_hash" IS NULL AND (b0."consensus" = TRUE))                                     | active

EXPLAIN ANALYZE on a small amount of the data:

Planning Time: 5.111 ms
Execution Time: 105251.312 ms

After the changes:

SELECT b0.* FROM
(SELECT * from "blocks" WHERE blocks."consensus" = TRUE) AS b0
LEFT OUTER JOIN
(SELECT * FROM "block_rewards"
WHERE block_rewards.address_type='validator') AS b1
ON b1."block_hash" = b0."hash"
WHERE b1."block_hash" IS NULL;

EXPLAIN ANALYZE on the same small set of the data, that it was before the changes:

Planning Time: 22.785 ms
Execution Time: 81535.140 ms

Checklist for your Pull Request (PR)

• I added an entry to CHANGELOG.md with this PR
• If I added new functionality, I added tests covering it.
• If I fixed a bug, I added a regression test to prevent the bug from silently reappearing again.
• I checked whether I should update the docs and did so by submitting a PR to https://github.com/blockscout/docs
• If I added/changed/removed ENV var, I submitted a PR to https://github.com/blockscout/docs to update the list of env vars at https://github.com/blockscout/docs/blob/master/for-developers/information-and-settings/env-variables.md and I updated the version to master in the Version column. Changes will be reflected in this table: https://docs.blockscout.com/for-developers/information-and-settings/env-variables.
• If I add new indices into DB, I checked, that they are not redundant with PGHero or other tools

[coveralls]

Pull Request Test Coverage Report for Build 2f80627e-8d31-4ac7-b03b-9b8a7f1fd9a2

• 2 of 2 (100.0%) changed or added relevant lines in 1 file are covered.
• 2 unchanged lines in 2 files lost coverage.
• Overall coverage increased (+0.007%) to 75.124%

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Files with Coverage Reduction	New Missed Lines	%
apps/block_scout_web/lib/block_scout_web/controllers/chain/market_history_chart_controller.ex	1	78.57%
apps/explorer/test/support/factory.ex	1	92.97%

Totals
Change from base Build e3430a1c-af77-4433-8eea-9d8c50b2a66b:	0.007%
Covered Lines:	5303
Relevant Lines:	7059

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💛 - Coveralls