3 ms·
Could you expand on this more columnar data and row data? I missed something here how the data is organized and what you mean by the C,D values getting dragged
by jzer0cool 6y ago
Could you expand on this more columnar data and row data? I missed something here how the data is organized and what you mean by the C,D values getting dragged along.
- int_19h 6y agoRow data is an array of structs, with each struct representing a record. Columnar data is a struct of arrays, with each array representing a column.
- repsilat 6y agoTo rephrase the sibling comment, if you had an array of four {ABCD} structs, there's basically two ways of storing them on disk: 1. AAAA BBBB CCCC DDDD 2. ABCD ABCD ABCD ABCD One major heuristic in how CPUs make your code fast is to assume that if you access some memory, you're probably interested in the memory nearby. So when you access the first "A" bit of memory (common to both sequences above), depending on the memory layout you use, the CPU might also be smart and load the next bits into memory too -- maybe the next "AA", maybe "BC". Depending on your workload, one or the other of those might be faster. If you're only interested in the first ABCD element because you're doing SELECT * FROM users WHERE id=$1 then you'll likely want "row-oriented" data -- the #2 scheme above. But if you're interested in all of the A values and none of the values from B/C/D because you're doing SELECT AVG(age) FROM users then you'll likely want something "column-oriented" -- the #1 scheme above.