Search Results
https://dev.mysql.com/doc/internals/en/optimizer-and-relations.html
An ANDed search has the form condition1 AND condition2, as in this example: WHERE column1 = 'x' AND column2 = 'y' Here, the optimizer's decision process can be described as follows: If (neither condition is indexed) use sequential scan. Otherwise, ...
https://dev.mysql.com/doc/internals/en/optimizer-eliminating-dead-code.html
A transformation takes place for conditions that are always true, for example: WHERE 0=0 AND column1='y' In this case, the first condition is removed, leaving WHERE column1='y' See: /sql/sql_select.cc, remove_eq_conds(). A transformation also takes ...
https://dev.mysql.com/doc/internals/en/optimizer-late-nulls-filtering.html
Suppose we have a query plan with table tblX being accessed via the ref access method: tblX.key_part1 = expr1 AND tblX.key_part2 = expr2 AND ... Before performing an index lookup, we determine whether any of the expri values is NULL. If it is, we ...
https://dev.mysql.com/doc/internals/en/optimizer-range-join-type.html
Some conditions can work with indexes, but over a (possibly wide) range of keys. The optimizer will use an index (range search) for column1 LIKE 'x%' but not for column1 LIKE '%x' That is, there is no range search if the first character in the ...
https://dev.mysql.com/doc/internals/en/packet-EOF_Packet.html
If CLIENT_PROTOCOL_41 is enabled, the EOF packet contains a warning count and status flags. Note In the MySQL client/server protocol, EOF and OK packets serve the same purpose, to mark the end of a query execution result. Due to changes in MySQL ...
https://dev.mysql.com/doc/internals/en/preventing-use-of-optimizer-trace.html
If for some reason, as DBA of a MySQL Server, you wish to prevent all users from seeing traces of their queries, start the server with these options: --maximum-optimizer-trace-max-mem-size=0 --optimizer-trace-max-mem-size=0 This sets the maximum ...
https://dev.mysql.com/doc/internals/en/protocoltext-resultset.html
A query like SELECT @@version_comment returns: 01 00 00 01 01|27 00 00 02 03 64 65 66 00 00 00 .....'....def... 11 40 40 76 65 72 73 69 6f 6e 5f 63 6f 6d 6d 65 .@@version_comme 6e 74 00 0c 08 00 1c 00 00 00 fd 00 00 1f 00 00| nt..............
https://dev.mysql.com/doc/internals/en/replication.html
Status of this section: up to date 2009-10-21 This chapter describes MySQL replication principles, rules, and code, as it is supposed to work in version 5.1. The MySQL replication feature allows a server - the master - to send all changes to ...
https://dev.mysql.com/doc/internals/en/row-order-within-result-sets.html
Please keep in mind that the row order within a significant number of result sets depends on storage engine properties and in worst cases the current load (NDB!, partitioning?, parallel query?) on the testing box. Either use --sorted_result SELECT ...
https://dev.mysql.com/doc/internals/en/select-subquery.html
In expressions, subqueries (that is, subselects) are represented by Item inherited from Item_subselect. To hide difference in performing single SELECTs and UNIONs, Item_subselect uses two different engines, which provide uniform interface for ...