SQL

success
SQL
SELECT region, COUNT(*) AS n, SUM(distance) AS total_distance
FROM trips
WHERE region = 'EU' AND trip_id > 2374
GROUP BY region

Dataset trips · ./data/trips

success 13.7 ms 1 row 16.5% of dataset bytes read Run #10 details
1 row 3 columns
Row regionntotal_distance
1 EU97,6251,960,572.36
Bytes scanned / dataset bytes
16.5%
1010.1 KB came off disk, out of 6.0 MB of compressed dataset bytes.
Execution
Duration 13.7 ms
Rows returned 1
Rows scanned 100000
Files pruned 10 of 15 files
Row-groups pruned 0 of 40 row-groups
Columns read 2 of 7 columns
Why it read that much
  • 10 of 15 files were never opened — the partition filter ruled them out from the directory path alone, costing zero I/O.
  • Only 2 of 7 columns came off disk — the other 5 were never referenced, and Parquet is columnar.
Where the bytes went
A naive full scan
6.0 MB
every byte of every column in every file
Files never opened
4.0 MB
partition values ruled them out from the path; zero I/O
Columns not referenced
1003.8 KB
Parquet is columnar, so these were never touched
Actually read
1010.1 KB
what came off disk to answer the query

The middle bars are bytes a scan-everything engine would have read and this one did not. They add up to the full scan exactly — it is one number decomposed, not four separate measurements.

Row-group map (40 of 40 read)
region=EU/date=2024-01-01
region=EU/date=2024-01-02
region=EU/date=2024-01-03
region=EU/date=2024-01-04
region=EU/date=2024-01-05
region=US/date=2024-01-01
never opened
region=US/date=2024-01-02
never opened
region=US/date=2024-01-03
never opened
region=US/date=2024-01-04
never opened
region=US/date=2024-01-05
never opened
region=APAC/date=2024-01-01
never opened
region=APAC/date=2024-01-02
never opened
region=APAC/date=2024-01-03
never opened
region=APAC/date=2024-01-04
never opened
region=APAC/date=2024-01-05
never opened
read skipped — footer stats proved no match file never opened, so its row-group count is unknown by design