Ruby on Rails，ActiveRecord，二进制搜索

Question

If I had the following table.

create_table :my_table, :id => false do |t|
   t.string :key_column
   t.string :value_column
end

How would I ensure that the rows are optimaly stored for binary search by the field of :key?

And how would I make sure binary search is used?

Answer 1

For any interesting number of rows, the optimal way (for most definitions of "optimal") to access a single random record by key is to create an index.

CREATE INDEX my_index ON my_table ( key_column );

or in an ActiveRecord migration:

add_index(:my_table, :key_column)

Database indices typically use binary search, using B-trees or similar, which offers a good balance between storage costs and time for retrieval and update.

Ensuring the index is used should be relatively straightforward for single-table operations:

MyTable.find_by_key_column('ABC123')

for example, should generate something like this (check development.log):

SELECT * FROM my_table WHERE (key_column = 'ABC123')

which even MySQL's relatively unimpressive optimiser should have no problem running optimally.

Row storage should not be a concern for individual row retrieval, which is fortunate as there isn't much you can do to control it anyway. For MySQL performance you should probably choose MyISAM over InnoDB as the storage engine, provided your definition of "optimal" doesn't include "most reliable".

Answer 2

It's the job of the database to accurately store and retrieve the data. You describe what you want, it delivers it. If you want to control specifically how it goes about doing so then a database is not the answer.