query-330bd4f2408370f0f71d9d76b99ec7c4

rq turtle/ttl

Equivalent queries and performance gotchas. select * where { # Query 1: 8475 rows (756 ms) #{ ?item wdt:P921 wd:Q202864 . } UNION { ?item wdt:P921 wd:Q8071861 . }

# Query 2: 8475 rows (796 ms) #values ?o { wd:Q202864 wd:Q8071861 } #?item wdt:P921 ?o .

# Query 3: 8475 rows (41529 ms) # why slow? theory: bad selectivity in first and only BGP making the query IO bound. # somehow the optimizer doesn't rewrite and consider only one part of the BGP known and not two. # results in initial cardinality of 29.5M instead of 16824. hint:Query hint:optimizer "Runtime" . ?item wdt:P921 ?o . filter (?o in (wd:Q202864, wd:Q8071861)) }

Use at

• https://query.wikidata.org/sparql

PREFIX wdt: <http://www.wikidata.org/prop/direct/>
PREFIX wd: <http://www.wikidata.org/entity/>
# Equivalent queries and performance gotchas.
select * where {
  # Query 1: 8475 rows (756 ms)
  #{ ?item wdt:P921 wd:Q202864 . } UNION { ?item wdt:P921 wd:Q8071861 . }

  # Query 2: 8475 rows (796 ms)
  #values ?o { wd:Q202864 wd:Q8071861 } 
  #?item wdt:P921 ?o .

  # Query 3: 8475 rows (41529 ms)
  # why slow? theory: bad selectivity in first and only BGP making the query IO bound.
  # somehow the optimizer doesn't rewrite and consider only one part of the BGP known and not two.
  # results in initial cardinality of 29.5M instead of 16824.

  ?item wdt:P921 ?o . filter (?o in (wd:Q202864, wd:Q8071861))
}

Query found at

• https://www.wikidata.org/wiki/Wikidata:Request_a_query/Archive/2024/03