P2. Which granules did the index discard?

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APPENDIX · P2 · INDEX · GO TO SLIDE 13

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EXPLAIN indexes = 1
SELECT count() FROM events
WHERE event_type = 'purchase'
  AND toDate(ts) = '2026-09-15';

EXPLAIN indexes = 1
SELECT count() FROM events
WHERE player_id = 1042;

What the result should be

-- первый запрос, фрагмент
MinMax      Parts: 1/3
            Granules: 301/624
PrimaryKey  Keys: event_type, toDate(ts)
            Granules: 1/301

-- второй запрос, фрагмент
PrimaryKey  Keys: player_id
            Granules: 220/624

MinMax by ts

Key prefix

Third column

Based on the minimum and maximum dates in each section, August and October were excluded—even before the initial index was calculated.

Key prefix condition: A search by tags returns one granule out of 301.

Checking tag ranges: 220 out of 624 tags were read.

The database contains three partitions: August, September, and October 1. So there are 624 granules, not 612 as shown on the slide13—before October was added.