… ms) That is index selectivity by condition (ID1=1) is V2/V1 = 0.3321 or 33.21% It is said (e.g. book “SQL Tuning”) if selectivity… index. Execution time: SELECT COUNT(SUBNAME) FROM t2 WHERE ID1=1 – 1200 ms SELECT COUNT(SUBNAME) FROM t2 IGNORE INDEX (ID1) WHERE ID1=1 – 260 ms…
Post: Why MySQL could be slow with large tables ?
June 9, 2006 By 141 Comments
… different in some respect and what works well for Oracle,MS SQL, PostgreSQL may not work well for MySQL and other way… also remember if indexes are helpful or not depends on index selectivity – how large proportion of rows matches to particular index value or range… 1..100 selects about 1% of the table. The times for full table scan vs range scan by index: mysql> select count(pad…
Post: Shard-Query EC2 images available
May 11, 2011 By 2 Comments
…: 1616904192 Max_data_length: 0 Index_length: 539279360 Data_free: 4194304 … ttl=61 time=0.637 ms … Note: There is no …, the third parse time). $ echo “select count(*) from ontime_fact;” | ./run_query Array ( [... shard-query/ $ ./run_query < queries.sql | tee raw |./pivot_results & [1] 12359 $ tail…
