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What is force index in MySQL?
The FORCE INDEX hint acts like USE INDEX ( index_list ) , with the addition that a table scan is assumed to be very expensive. In other words, a table scan is used only if there is no way to use one of the named indexes to find rows in the table. As of MySQL 8.0. It can be an unambiguous prefix of an index name.
What’s the difference between index and primary key?
A primary key is a logical concept. The primary key are the column(s) that serves to identify the rows. An index is a physical concept and serves as a means to locate rows faster, but is not intended to define rules for the table.
What is the range dive limit in MySQL?
The eq_range_index_dive_limit system variable enables you to configure the number of values at which the optimizer switches from one row estimation strategy to the other. To permit use of index dives for comparisons of up to N equality ranges, set eq_range_index_dive_limit to N + 1.
When to use a range optimizer in MySQL?
The optimizer attempts to use additional key parts to determine the interval as long as the comparison operator is = , <=> , or IS NULL. If the operator is > , < , >= , <= , != , <> , BETWEEN, or LIKE, the optimizer uses it but considers no more key parts.
When do you use range access in MySQL?
The range access method uses a single index to retrieve a subset of table rows that are contained within one or several index value intervals. It can be used for a single-part or multiple-part index. The following sections describe conditions under which the optimizer uses range access.
How to control the memory available to the range optimizer?
To control the memory available to the range optimizer, use the range_optimizer_max_mem_size system variable: A value of 0 means “no limit.” With a value greater than 0, the optimizer tracks the memory consumed when considering the range access method.