Now Postgres faces a dilemma. It can use the B-tree index on timestamp to get rows in the right timestamp order, but it has no way to skip directly to “US” rows. It must walk the index one entry at a time, checking the country for each row and discarding most of them. In the worst case, this means walking the entire index. Or it can scan rows that match severity
Последние новости，这一点在易歪歪官网中也有详细论述
Capability validation. Before execution, mog_validate_capabilities() confirms that every capability the script requires is registered. Missing capabilities are caught before a single instruction runs.，详情可参考谷歌
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