A few customers with rather extreme needs have contacted us about
a performance issue with the range optimizer. Our solution to the
problem is to introduce a new variable in MySQL 5.6,
eq_range_index_dive_limit, which can be used to control whether
or not the range optimizer will a) do index dives, or b) use
index statistics when estimating the number of rows in the ranges
of the query. The former method gives a far more accurate
estimate while the latter costs a lot less to compute.
This is what the help text has to tell about the variable:
The optimizer will use existing index statistics instead of doing
index dives for equality ranges if the number of equality ranges
for the index is larger than or equal to [the value of variable].
If set to 0, index dives are always used."Equality range" means
predicates using operators IN() or =, and it's important to
notice that the number of such ranges is counted on a per index …
Showing entries 1 to 1
Apr
10
2012
Showing entries 1 to 1