Eric Luo lxneng

PySpark on YARN in self-contained environments

Don’t SELECT *, Specify explicit column names (columnar store)
Avoid large JOINs (filter each table first)
- In PRESTO tables are joined in the order they are listed!!
- Join small tables earlier in the plan and leave larger fact tables to the end
- Avoid cross joins or 1 to many joins as these can degrade performance
Order by and group by take time
- only use order by in subqueries if it is really necessary
When using GROUP BY, order the columns by the highest cardinality (that is, most number of unique values) to the lowest.

Note: "Forked" from Latency Numbers Every Programmer Should Know

Event	Nanoseconds	Microseconds	Milliseconds	Comparison
L1 cache reference	0.5	-	-	-
Branch mispredict	5.0	-	-	-
L2 cache reference	7.0	-	-	14x L1 cache
Mutex lock/unlock	25.0	-	-	-

	import streamlit as st
	import os
	import sys
	import importlib.util

	# Parse command-line arguments.
	if len(sys.argv) > 1:
	folder = os.path.abspath(sys.argv[1])
	else:
	folder = os.path.abspath(os.getcwd())

	Latency Comparison Numbers (~2012)
	----------------------------------
	L1 cache reference 0.5 ns
	Branch mispredict 5 ns
	L2 cache reference 7 ns 14x L1 cache
	Mutex lock/unlock 25 ns
	Main memory reference 100 ns 20x L2 cache, 200x L1 cache
	Compress 1K bytes with Zippy 3,000 ns 3 us
	Send 1K bytes over 1 Gbps network 10,000 ns 10 us
	Read 4K randomly from SSD* 150,000 ns 150 us ~1GB/sec SSD