Massive cleanups to internals.texi.

\input texinfo  @c -*-texinfo-*-

@c Copyright 1998 TcX AB, Detron HB and Monty Program KB

@c Copyright 2002 MySQL AB, TcX AB, Detron HB and Monty Program KB

@c

@c %**start of header

@setfilename internals.info

@c We want the types in the same index

@c @synindex tp fn cp

@synindex cp fn

@iftex

@c Well this is normal in Europe. Maybe this should go into the include.texi?

@afourpaper

@end iftex

@c Get version and other info

@include include.texi

@ifclear tex-debug

@c This removes the black squares in the right margin

@finalout

@end ifclear

@c Set background for HTML

@set _body_tags BGCOLOR=#FFFFFF TEXT=#000000 LINK=#101090 VLINK=#7030B0

@settitle @strong{MySQL} internals Manual for version @value{mysql_version}.

@setchapternewpage off

@settitle @strong{MySQL} Internals Manual for version @value{mysql_version}.

@setchapternewpage odd

@paragraphindent 0

@c %**end of header

@ifinfo

@sp 10

@center @titlefont{@strong{MySQL} Internals Manual}

@sp 10

@center Copyright @copyright{} 1998 TcX AB, Detron HB and Monty Program KB

@center Copyright @copyright{} 1998-2002 MySQL AB

@page

@end titlepage

@node Top, Introduction, (dir), (dir)

@node Top, caching, (dir), (dir)

@ifinfo

This is a manual about @strong{MySQL} internals.

@end ifinfo

@menu

* caching::                     How MySQL Handles Caching

* flush tables::                How MySQL Handles @code{FLUSH TABLES}

* filesort::                    How MySQL Does Sorting (@code{filesort})

* coding guidelines::           Coding Guidelines

* mysys functions::             Functions In The @code{mysys} Library

* DBUG::                        DBUG Tags To Use

* protocol::                    MySQL Client/Server Protocol

@end menu

@node caching,,,

@chapter How MySQL handles caching

@node caching, flush tables, Top, Top

@chapter How MySQL Handles Caching

@strong{MySQL} has the following caches:

(Note that the some of the filename have a wrong spelling of cache. :)

@itemize @bullet

@table @strong

@item Key cache

@item Key Cache

A shared cache for all B-tree index blocks in the different NISAM

files. Uses hashing and reverse linked lists for quick caching of the

last used blocks and quick flushing of changed entries for a specific

table. (@file{mysys/mf_keycash.c})

@item Record cache

@item Record Cache

This is used for quick scanning of all records in a table.

(@file{mysys/mf_iocash.c} and @file{isam/_cash.c})

@item Table cache

@item Table Cache

This holds the last used tables. (@file{sql/sql_base.cc})

@item Hostname cache

@item Hostname Cache

For quick lookup (with reverse name resolving). Is a must when one has a

slow DNS. 

(@file{sql/hostname.cc})

@item Privilege cache

@item Privilege Cache

To allow quick change between databases the last used privileges are

cached for each user/database combination.

(@file{sql/sql_acl.cc})

@item Heap table cache

Many use of GROUP BY or DISTINCT caches all found

rows in a HEAP table (this is a very quick in-memory table with hash index)

@item Heap Table Cache

Many use of @code{GROUP BY} or @code{DISTINCT} caches all found rows in 

a @code{HEAP} table. (This is a very quick in-memory table with hash index.)

@item Join row cache.

For every full join in a SELECT statement (a full join here means there

were no keys that one could use to find the next table in a list), the

found rows are cached in a join cache.  One SELECT query can use many

join caches in the worst case.

@end itemize

@item Join Row Cache

For every full join in a @code{SELECT} statement (a full join here means

there were no keys that one could use to find the next table in a list), 

the found rows are cached in a join cache.  One @code{SELECT} query can 

use many join caches in the worst case.

@end table

@node flush tables,,,

@chapter How MySQL handles flush tables

@node flush tables, filesort, caching, Top

@chapter How MySQL Handles @code{FLUSH TABLES}

@itemize @bullet

@item

Flush tables is handled in @code{sql/sql_base.cc::close_cached_tables()}.

Flush tables is handled in @file{sql/sql_base.cc::close_cached_tables()}.

@item

The idea of flush tables is to force all tables to be closed. This

When one does a @code{FLUSH TABLES}, the variable @code{refresh_version} 

will be incremented. Every time a thread releases a table it checks if

the refresh version of the table (updated at open) is the same as

the current refresh_version.  If not it will close it and broadcast

a signal on COND_refresh (to wait any thread that is waiting for

the current @code{refresh_version}.  If not it will close it and broadcast

a signal on @code{COND_refresh} (to wait any thread that is waiting for

all instanses of a table to be closed).

@item

refresh version is different the thread will free all locks, reopen the

table and try to get the locks again;  This is just to quickly get all 

tables to use the newest version.  This is handled by

@code{sql/lock.cc::mysql_lock_tables()} and 

@code{sql/sql_base.cc::wait_for_tables()}.

@file{sql/lock.cc::mysql_lock_tables()} and 

@file{sql/sql_base.cc::wait_for_tables()}.

@item

When all tables has been closed @code{FLUSH TABLES} will return an ok 

@end itemize

@node Filesort,,,

@chapter How MySQL does sorting (filesort)

@node filesort, coding guidelines, flush tables, Top

@chapter How MySQL Does Sorting (@code{filesort})

@itemize @bullet

Store the sort-key in a buffer (@code{sort_buffer}).

@item

When the buffer gets full, run a qsort on it and store the result

When the buffer gets full, run a @code{qsort} on it and store the result

in a temporary file.  Save a pointer to the sorted block.

@item

@end itemize

@node Coding guidelines,,,

@chapter Coding guidelines

@node coding guidelines, mysys functions, filesort, Top

@chapter Coding Guidelines

@itemize @bullet

Do not check the same pointer for @code{NULL} more than once.

@item

Use long function and variable names in English; This makes your code

Use long function and variable names in English.  This makes your code

easier to read. 

@item

Use my_var as opposed to myVar or MyVar (@samp{_} rather than dancing SHIFT

to seperate words in identifiers).

Use @code{my_var} as opposed to @code{myVar} or @code{MyVar} (@samp{_} 

rather than dancing SHIFT to seperate words in identifiers).

@item

Think assembly - make it easier for the compiler to optimize your code.

@item

Comment your code when you do something that someone else may think

is not ''trivial''.

is not ``trivial''.

@item

Use @code{libstring} functions (in the strings directory)

instead of standard libc string functions whenever possible.

Use @code{libstring} functions (in the @file{strings} directory)

instead of standard @code{libc} string functions whenever possible.

@item

Avoid using @code{malloc()} (its REAL slow);  For memory allocations 

Matching @samp{@{} are in the same column.

@item

Put the @samp{@{} after a 'switch' on the same line

Put the @samp{@{} after a @code{switch} on the same line, as this gives 

better overall indentation for the switch statement:

@example

switch (arg) {

@end example

Because this gives better overall indentation for the switch statement.

@item

In all other cases, @{ and @} should be on their own line, except

if there is nothing inside @{ @}.

In all other cases, @samp{@{} and @samp{@}} should be on their own line, except

if there is nothing inside @samp{@{} and @samp{@}}.

@item

Have a space after 'if'

Have a space after @code{if}

@item

Put a space after ',' for function arguments

Put a space after @samp{,} for function arguments

@item

Functions return 0 on success, and non-zero on error, so you can do:

Functions return @samp{0} on success, and non-zero on error, so you can do:

@example

if(a() || b() || c()) { error("something went wrong"); }

(setq c-default-style "MY")

@end example

@node mysys functions,,,

@chapter mysys functions

Functions i mysys: (For flags se my_sys.h)

 int my_copy _A((const char *from,const char *to,myf MyFlags));

	- Copy file

 int my_delete _A((const char *name,myf MyFlags));

	- Delete file

 int my_getwd _A((string buf,uint size,myf MyFlags));

 int my_setwd _A((const char *dir,myf MyFlags));

	- Get and set working directory

 string my_tempnam _A((const char *pfx,myf MyFlags));

	- Make a uniq temp file name by using dir and adding something after

	 pfx to make name uniq. Name is made by adding a uniq 6 length-string

	 and TMP_EXT after pfx.

	 Returns pointer to malloced area for filename. Should be freed by

	 free().

 File my_open _A((const char *FileName,int Flags,myf MyFlags));

 File my_create _A((const char *FileName,int CreateFlags,

			  int AccsesFlags, myf MyFlags));

 int my_close _A((File Filedes,myf MyFlags));

 uint my_read _A((File Filedes,byte *Buffer,uint Count,myf MyFlags));

 uint my_write _A((File Filedes,const byte *Buffer,uint Count,

			 myf MyFlags));

 ulong my_seek _A((File fd,ulong pos,int whence,myf MyFlags));

 ulong my_tell _A((File fd,myf MyFlags));

	- Use instead of open,open-with-create-flag, close read and write

	  to get automatic error-messages (flag: MYF_WME) and only have

	  to test for != 0 if error (flag: MY_NABP).

 int my_rename _A((const char *from,const char *to,myf MyFlags));

	- Rename file

 FILE *my_fopen _A((const char *FileName,int Flags,myf MyFlags));

 FILE *my_fdopen _A((File Filedes,int Flags,myf MyFlags));

 int my_fclose _A((FILE *fd,myf MyFlags));

 uint my_fread _A((FILE *stream,byte *Buffer,uint Count,myf MyFlags));

 uint my_fwrite _A((FILE *stream,const byte *Buffer,uint Count,

			  myf MyFlags));

 ulong my_fseek _A((FILE *stream,ulong pos,int whence,myf MyFlags));

 ulong my_ftell _A((FILE *stream,myf MyFlags));

	- Same read-interface for streams as for files

 gptr _mymalloc _A((uint uSize,const char *sFile,

			  uint uLine, myf MyFlag));

 gptr _myrealloc _A((string pPtr,uint uSize,const char *sFile,

			   uint uLine, myf MyFlag));

 void _myfree _A((gptr pPtr,const char *sFile,uint uLine));

 int _sanity _A((const char *sFile,unsigned int uLine));

 gptr _myget_copy_of_memory _A((const byte *from,uint length,

				      const char *sFile, uint uLine,

				      myf MyFlag));

	- malloc(size,myflag) is mapped to this functions if not compiled

	  with -DSAFEMALLOC

 void TERMINATE _A((void));

	- Writes malloc-info on stdout if compiled with -DSAFEMALLOC.

 int my_chsize _A((File fd,ulong newlength,myf MyFlags));

	- Change size of file

 void my_error _D((int nr,myf MyFlags, ...));

	- Writes message using error number (se mysys/errors.h) on

	  stdout or curses if  MYSYS_PROGRAM_USES_CURSES() is called.

 void my_message _A((const char *str,myf MyFlags));

	- Writes message-string on

	 stdout or curses if  MYSYS_PROGRAM_USES_CURSES() is called.

 void my_init _A((void ));

	- Start each program (in main) with this.

 void my_end _A((int infoflag));

	- Gives info about program.

	- If infoflag & MY_CHECK_ERROR prints if some files are left open

	- If infoflag & MY_GIVE_INFO   prints timing info and malloc info

	  about prog.

 int my_redel _A((const char *from, const char *to, int MyFlags));

	- Delete from before rename of to to from. Copyes state from old

	  file to new file. If MY_COPY_TIME is set sets old time.

 int my_copystat _A((const char *from, const char *to, int MyFlags));

	- Copye state from old file to new file.

	  If MY_COPY_TIME is set sets copy also time.

 string my_filename _A((File fd));

	- Give filename of open file.

 int dirname _A((string to,const char *name));

	- Copy name of directory from filename.

 int test_if_hard_path _A((const char *dir_name));

	- Test if dirname is a hard path (Starts from root)

 void convert_dirname _A((string name));

	- Convert dirname acording to system.

	  - In MSDOS changes all caracters to capitals and changes '/' to

	    '\'

 string fn_ext _A((const char *name));

	- Returns pointer to extension in filename

 string fn_format _A((string to,const char *name,const char *dsk,

			    const char *form,int flag));

@node mysys functions, DBUG, coding guidelines, Top

@chapter Functions In The @code{mysys} Library

Functions in @code{mysys}: (For flags see @file{my_sys.h})

@table @code

@item int my_copy _A((const char *from, const char *to, myf MyFlags));

Copy file from @code{from} to @code{to}.

@item int my_delete _A((const char *name, myf MyFlags));

Delete file @code{name}.

@item int my_getwd _A((string buf, uint size, myf MyFlags));

@item int my_setwd _A((const char *dir, myf MyFlags));

Get and set working directory.

@item string my_tempnam _A((const char *pfx, myf MyFlags));

Make a unique temporary file name by using dir and adding something after

@code{pfx} to make name unique.  The file name is made by adding a unique

six character string and @code{TMP_EXT} after @code{pfx}.

Returns pointer to @code{malloc()}'ed area for filename. Should be freed by

@code{free()}.

@item File my_open _A((const char *FileName,int Flags,myf MyFlags));

@item File my_create _A((const char *FileName, int CreateFlags, int AccsesFlags, myf MyFlags));

@item int my_close _A((File Filedes, myf MyFlags));

@item uint my_read _A((File Filedes, byte *Buffer, uint Count, myf MyFlags));

@item uint my_write _A((File Filedes, const byte *Buffer, uint Count, myf MyFlags));

@item ulong my_seek _A((File fd,ulong pos,int whence,myf MyFlags));

@item ulong my_tell _A((File fd,myf MyFlags));

Use instead of open, open-with-create-flag, close, read, and write

to get automatic error messages (flag @code{MYF_WME}) and only have

to test for != 0 if error (flag @code{MY_NABP}).

@item int my_rename _A((const char *from, const char *to, myf MyFlags));

Rename file from @code{from} to @code{to}.

@item FILE *my_fopen _A((const char *FileName,int Flags,myf MyFlags));

@item FILE *my_fdopen _A((File Filedes,int Flags,myf MyFlags));

@item int my_fclose _A((FILE *fd,myf MyFlags));

@item uint my_fread _A((FILE *stream,byte *Buffer,uint Count,myf MyFlags));

@item uint my_fwrite _A((FILE *stream,const byte *Buffer,uint Count, myf MyFlags));

@item ulong my_fseek _A((FILE *stream,ulong pos,int whence,myf MyFlags));

@item ulong my_ftell _A((FILE *stream,myf MyFlags));

Same read-interface for streams as for files.

@item gptr _mymalloc _A((uint uSize,const char *sFile,uint uLine, myf MyFlag));

@item gptr _myrealloc _A((string pPtr,uint uSize,const char *sFile,uint uLine, myf MyFlag));

@item void _myfree _A((gptr pPtr,const char *sFile,uint uLine));

@item int _sanity _A((const char *sFile,unsigned int uLine));

@item gptr _myget_copy_of_memory _A((const byte *from,uint length,const char *sFile, uint uLine,myf MyFlag));

@code{malloc(size,myflag)} is mapped to these functions if not compiled 

with @code{-DSAFEMALLOC}.

@item void TERMINATE _A((void));

Writes @code{malloc()} info on @code{stdout} if compiled with 

@code{-DSAFEMALLOC}.

@item int my_chsize _A((File fd, ulong newlength, myf MyFlags));

Change size of file @code{fd} to @code{newlength}.

@item void my_error _D((int nr, myf MyFlags, ...));

Writes message using error number (see @file{mysys/errors.h}) on @code{stdout},

or using curses, if @code{MYSYS_PROGRAM_USES_CURSES()} has been called.

@item void my_message _A((const char *str, myf MyFlags));

Writes @code{str} on @code{stdout}, or using curses, if 

@code{MYSYS_PROGRAM_USES_CURSES()} has been called.

@item void my_init _A((void ));

Start each program (in @code{main()}) with this.

@item void my_end _A((int infoflag));

Gives info about program.

If @code{infoflag & MY_CHECK_ERROR}, prints if some files are left open.

If @code{infoflag & MY_GIVE_INFO}, prints timing info and malloc info

about program.

@item int my_redel _A((const char *from, const char *to, int MyFlags));

Delete @code{from} before rename of @code{to} to @code{from}.  Copies state

from old file to new file. If @code{MY_COPY_TIME} is set, sets old time.

@item int my_copystat _A((const char *from, const char *to, int MyFlags));

Copy state from old file to new file.  If @code{MY_COPY_TIME} is set,

sets old time.

@item string my_filename _A((File fd));

Returns filename of open file.

@item int dirname _A((string to, const char *name));

Copy name of directory from filename.

@item int test_if_hard_path _A((const char *dir_name));

Test if @code{dir_name} is a hard path (starts from root).

@item void convert_dirname _A((string name));

Convert dirname according to system.

In MSDOS, changes all characters to capitals and changes @samp{/} to @samp{\}.

@item string fn_ext _A((const char *name));

Returns pointer to extension in filename.

@item string fn_format _A((string to,const char *name,const char *dsk,const char *form,int flag));

	format a filename with replace of library and extension and

	converts between different systems.

	params to and name may be identicall

	"open(fn_format(temp_buffe,name,"","",4),...)" to unpack home and

	convert filename to system-form.

 string fn_same _A((string toname,const char *name,int flag));

	- Copys directory and extension from name to toname if neaded.

	  copy can be forced by same flags that in fn_format.

@item string fn_same _A((string toname, const char *name, int flag));

Copys directory and extension from @code{name} to @code{toname} if neaded.

Copying can be forced by same flags used in @code{fn_format()}.

 int wild_compare _A((const char *str,const char *wildstr));

	- Compare if str matches wildstr. Wildstr can contain "*" and "?"

	  as match-characters.

	  Returns 0 if match.

@item int wild_compare _A((const char *str, const char *wildstr));

Compare if @code{str} matches @code{wildstr}. @code{wildstr} can contain 

@samp{*} and @samp{?} as wildcard characters.

Returns 0 if @code{str} and @code{wildstr} match.

 void get_date _A((string to,int timeflag));

	- Get current date in a form ready for printing.

@item void get_date _A((string to, int timeflag));

Get current date in a form ready for printing.

 void soundex _A((string out_pntr, string in_pntr))

	- Makes in_pntr to a 5 chars long string. All words that sounds

@item void soundex _A((string out_pntr, string in_pntr))

Makes @code{in_pntr} to a 5 char long string.  All words that sound

alike have the same string.

 int init_key_cache _A((ulong use_mem,ulong leave_this_much_mem));

	- Use cacheing of keys in MISAM, PISAM, and ISAM.

	  KEY_CACHE_SIZE is a good size.

	  - Remember to lock databases for optimal cacheing

@item int init_key_cache _A((ulong use_mem, ulong leave_this_much_mem));

Use caching of keys in MISAM, PISAM, and ISAM.

@code{KEY_CACHE_SIZE} is a good size.

Remember to lock databases for optimal caching.

@item void end_key_cache _A((void));

End key caching.

 void end_key_cache _A((void));

	- End key-cacheing.

@node DBUG,,,

@chapter The DBUG tags to use:

@node DBUG, protocol, mysys functions, Top

@chapter DBUG Tags To Use

Here is some of the tags we now use:

(We should probably add a couple of new ones)

"enter"	  Arguments to the function.

"exit"	  Results from the function.

"info"    is something that may be interesting.

"warning" is when something doesn't go the usual route or may be wrong.

"error"   when something went wrong.

"loop"	  write in a loop, that is probably only useful when debugging

	  the loop.  These should normally be deleted when on is

@table @code 

@item enter

Arguments to the function.

@item exit

Results from the function.

@item info

Something that may be interesting.

@item warning

When something doesn't go the usual route or may be wrong.

@item error

When something went wrong.

@item loop

Write in a loop, that is probably only useful when debugging

the loop.  These should normally be deleted when one is

satisfied with the code and it has been in real use for a while.

@end table

Some specific to mysqld, because we want to watch these carefully:

"trans"	  Starting/stopping transactions.

"quit"	  'info' when mysqld is preparing to die.

"query"	  Print query

@table @code

@item trans

Starting/stopping transactions.

@item quit

@code{info} when mysqld is preparing to die.

@item query

Print query.

@end table

@node protocol,  , DBUG, Top

@chapter MySQL Client/Server Protocol

@menu

* raw packet without compression::  

* raw packet with compression::  

* basic packets::               

* communication::               

* fieldtype codes::             

@end menu

@node protocol,,,

@chapter MySQL client/server protocol

@node raw packet without compression, raw packet with compression, protocol, protocol

@section Raw Packet Without Compression

Raw packet without compression

============================== 	

@example

-------------------------------------------------

| Packet Length	| Packet no 	| Data		|

| 3 Bytes	| 1 Byte 	| n Bytes	|

-------------------------------------------------

@end example

3 Byte packet length

  The length is calculated with int3store

The packet length can be recalculated with:

length = byte1 + (256 * byte2) + (256 * 256 * byte3)

Raw packet with compression

=========================== 	

@node raw packet with compression, basic packets, raw packet without compression, protocol

@section Raw Packet With Compression

@example

-----------------------------------------------------

| Packet Length	| Packet no | Uncomp. Packet Length |

| 3 Bytes	| 1 Byte    | 3 Bytes		    |

-----------------------------------------------------

@end example

3 Byte packet length

  The length is calculated with int3store

1 Byte packet no

3 Byte uncompressed packet length

If compression is used the first 7 bytes of each paket

is the header of the paket.

If compression is used the first 7 bytes of each packet

is the header of the packet.

@node basic packets, communication, raw packet with compression, protocol

@section Basic Packets

@menu

* ok packet::                   

* error packet::                

@end menu

@node ok packet, error packet, basic packets, basic packets

@subsection OK Packet

Basic packets

==============

OK-packet	

	For details see sql/net_pkg.cc

	function send_ok

@example

	-------------------------------------------------

	| Header	| No of Rows 	| Affected Rows |

	| 		| 1 Byte 	| 1-8 Byte	|

	| Messagetext					|

	| n Byte					|

	-------------------------------------------------

@end example

	Header

	1 byte number of rows ? (always 0 ?)

	1-8 bytes length of message

	n bytes messagetext

Error-packet	

@node error packet,  , ok packet, basic packets

@subsection Error Packet	

@example

	-------------------------------------------------

	| Header	| Statuscode	| Error no	|

	| 		| 1 Byte 	| 2 Byte	|

	| Messagetext			       | 0x00	|

	| n Byte			       | 1 Byte |

	-------------------------------------------------

@end example

	Header

	1 byte status code (0xFF = ERROR)

	1 byte 0x00

The communication

=================

@node communication, fieldtype codes, basic packets, protocol

@section Communication

> Packet from server to client

< Paket from client tor server

		n data

Fieldtype Codes:

================

@node fieldtype codes,  , communication, protocol

@section Fieldtype Codes

@example

		display_length 	|enum_field_type	|flags

		----------------------------------------------------

Blob		03 FF FF 00	|01 FC			|03 90 00 00

Timestamp	03 0E 00 00	|01 07			|03 61 04 00

Time		03 08 00 00	|01 0B			|03 00 00 00

Date		03 0A 00 00	|01 0A			|03 00 00 00

@end example

@c The Index was empty, and ugly, so I removed it. (jcole, Sep 7, 2000)