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https://dev.mysql.com/doc/internals/en/multi-statement.html
A multi-statement is permitting COM_QUERY to send more than one query to the server, separated by ';' characters. The client must announce that it wants multi-statements by either setting the CLIENT_MULTI_STATEMENTS capability or by using ...
https://dev.mysql.com/doc/internals/en/open.html
A handler object is opened as part of its initialization and before being used for normal queries (not before meta-data changes always.) If the object was opened it will also be closed before being deleted. Synopsis virtual int open ( name, mode, ...
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 ...