JAllemandou added a comment.
Exact analysis ran on 2018-12-06:
val df =
spark.read.parquet("/user/joal/wmf/data/wmf/mediawiki/wikidata_parquet/20181001")
val base_rdd = df.select("labels", "descriptions", "aliases").rdd
val strings = base_rdd.flatMap(r => {
r.getMap[String,String](0).values ++
r.getMap[String,String](1).values ++
r.getMap[String,Seq[String]](2).values.flatMap(l => l)
})
val grouped_strings = strings.map(s => (s, 1)).reduceByKey(_+_)
val total_bytes = grouped_strings.map(t => t._1.getBytes.length *
t._2).sum()
val duplicate_bytes = grouped_strings.map(t => t._1.getBytes.length * (t._2
- 1)).sum()
println(f"Total bytes for strings: $total_bytes%15.0f")
println(f"Total duplicate bytes for strings: $duplicate_bytes%15.0f")
println(f"Usefull bytes for strings: ${total_bytes -
duplicate_bytes}%15.0f")
//Total bytes for strings: 45,724,033,674
//Total duplicate bytes for strings: 41,630,588,801
//Usefull bytes for strings: 4,093,444,873
// Usefull is 1 order of magnitude less than used
// Triple check usefull bytes for strings:
grouped_strings.map(_._1.getBytes.length).sum() == (total_bytes -
duplicate_bytes)
// true
// How many unique strings?
grouped_strings.count()
// 98,524,732
// How many string with 1 instance?
grouped_strings.filter(t => t._2 == 1).count()
// 72,584,179
// Leaving 25,940,553 unique strings having multiple instances
// --> If we go for table-indirection, we'll need ~100M longs (4 bytes)
// --> 400,000,000 bytes - 1 order of magnitude less than unique string
size
TASK DETAIL
https://phabricator.wikimedia.org/T217821
EMAIL PREFERENCES
https://phabricator.wikimedia.org/settings/panel/emailpreferences/
To: JAllemandou
Cc: JAllemandou, Aklapper, Addshore, alaa_wmde, Nandana, Lahi, Gq86,
GoranSMilovanovic, QZanden, LawExplorer, _jensen, rosalieper, Wikidata-bugs,
aude, Mbch331
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