internals.texi 19.1 KB
Newer Older
bk@work.mysql.com's avatar
bk@work.mysql.com committed
1 2 3 4 5 6 7 8 9
\input texinfo  @c -*-texinfo-*-
@c Copyright 1998 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
10
@c Well this is normal in Europe. Maybe this should go into the include.texi?
bk@work.mysql.com's avatar
bk@work.mysql.com committed
11 12 13 14 15 16 17 18 19 20 21 22
@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
23
@paragraphindent 0
bk@work.mysql.com's avatar
bk@work.mysql.com committed
24 25 26 27 28 29 30 31 32 33 34 35
@c %**end of header

@ifinfo
@format
START-INFO-DIR-ENTRY
* mysql-internals: (mysql-internals).               @strong{MySQL} internals.
END-INFO-DIR-ENTRY
@end format
@end ifinfo

@titlepage
@sp 10
36
@center @titlefont{@strong{MySQL} Internals Manual}
bk@work.mysql.com's avatar
bk@work.mysql.com committed
37 38 39 40 41 42 43 44 45 46 47 48 49
@sp 10
@center Copyright @copyright{} 1998 TcX AB, Detron HB and Monty Program KB
@end titlepage

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

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

@menu
@end menu

50
@node caching,,,
51
@chapter How MySQL handles caching
bk@work.mysql.com's avatar
bk@work.mysql.com committed
52

53
@strong{MySQL} has the following caches:
54
(Note that the some of the filename have a wrong spelling of cache. :)
bk@work.mysql.com's avatar
bk@work.mysql.com committed
55 56

@itemize @bullet
57

bk@work.mysql.com's avatar
bk@work.mysql.com committed
58 59 60 61
@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
62
table. (@file{mysys/mf_keycash.c})
bk@work.mysql.com's avatar
bk@work.mysql.com committed
63 64 65

@item Record cache
This is used for quick scanning of all records in a table.
66
(@file{mysys/mf_iocash.c} and @file{isam/_cash.c})
bk@work.mysql.com's avatar
bk@work.mysql.com committed
67 68

@item Table cache
69
This holds the last used tables. (@file{sql/sql_base.cc})
bk@work.mysql.com's avatar
bk@work.mysql.com committed
70 71 72

@item Hostname cache
For quick lookup (with reverse name resolving). Is a must when one has a
73 74
slow DNS. 
(@file{sql/hostname.cc})
bk@work.mysql.com's avatar
bk@work.mysql.com committed
75 76 77

@item Privilege cache
To allow quick change between databases the last used privileges are
78 79
cached for each user/database combination.
(@file{sql/sql_acl.cc})
bk@work.mysql.com's avatar
bk@work.mysql.com committed
80 81 82

@item Heap table cache
Many use of GROUP BY or DISTINCT caches all found
83
rows in a HEAP table (this is a very quick in-memory table with hash index)
bk@work.mysql.com's avatar
bk@work.mysql.com committed
84 85 86

@item Join row cache.
For every full join in a SELECT statement (a full join here means there
87
were no keys that one could use to find the next table in a list), the
bk@work.mysql.com's avatar
bk@work.mysql.com committed
88 89 90 91
found rows are cached in a join cache.  One SELECT query can use many
join caches in the worst case.
@end itemize

92
@node flush tables,,,
93
@chapter How MySQL handles flush tables
bk@work.mysql.com's avatar
bk@work.mysql.com committed
94 95

@itemize @bullet
96 97 98 99

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

bk@work.mysql.com's avatar
bk@work.mysql.com committed
100 101 102
@item
The idea of flush tables is to force all tables to be closed. This
is mainly to ensure that if someone adds a new table outside of
103 104 105 106 107
@strong{MySQL} (for example with @code{cp}) all threads will start using 
the new table. This will also ensure that all table changes are flushed 
to disk (but of course not as optimally as simple calling a sync on
all tables)!

bk@work.mysql.com's avatar
bk@work.mysql.com committed
108
@item
109 110
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
bk@work.mysql.com's avatar
bk@work.mysql.com committed
111 112 113 114
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
all instanses of a table to be closed).
115

bk@work.mysql.com's avatar
bk@work.mysql.com committed
116
@item
117 118 119 120 121 122 123 124
The current @code{refresh_version} is also compared to the open 
@code{refresh_version} after a thread gets a lock on a table.  If the 
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()}.

bk@work.mysql.com's avatar
bk@work.mysql.com committed
125
@item
126 127 128
When all tables has been closed @code{FLUSH TABLES} will return an ok 
to client.

bk@work.mysql.com's avatar
bk@work.mysql.com committed
129
@item
130 131 132 133 134
If the thread that is doing @code{FLUSH TABLES} has a lock on some tables,
it will first close the locked tables, then wait until all other threads
have also closed them, and then reopen them and get the locks.
After this it will give other threads a chance to open the same tables.

bk@work.mysql.com's avatar
bk@work.mysql.com committed
135 136
@end itemize

137
@node Filesort,,,
138
@chapter How MySQL does sorting (filesort)
139

140 141 142 143 144 145 146 147 148 149 150 151 152 153 154 155 156 157 158 159 160 161 162 163 164 165 166 167 168 169 170 171 172 173 174 175
@itemize @bullet

@item
Read all rows according to key or by table scanning.

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

@item
Repeat the above until all rows have been read.

@item
Repeat the following until there is less than @code{MERGEBUFF2} (15) 
blocks left.

@item
Do a multi-merge of up to @code{MERGEBUFF} (7) regions to one block in
another temporary file.  Repeat until all blocks from the first file
are in the second file.

@item
On the last multi-merge, only the pointer to the row (last part of
the sort-key) is written to a result file.

@item
Now the code in @file{sql/records.cc} will be used to read through them
in sorted order by using the row pointers in the result file.
To optimize this, we read in a big block of row pointers, sort these
and then we read the rows in the sorted order into a row buffer
(@code{record_buffer}) .

@end itemize
176

177
@node Coding guidelines,,,
178 179
@chapter Coding guidelines

180 181 182 183 184 185 186 187 188 189 190 191 192 193 194 195 196 197 198 199 200 201 202 203 204 205 206 207 208 209 210 211 212 213 214 215 216 217 218 219 220 221 222 223 224 225 226 227 228 229 230 231 232 233 234 235 236 237 238 239 240 241 242 243 244 245 246 247 248 249 250 251 252 253 254 255 256 257 258 259 260 261 262 263 264 265 266 267 268 269 270 271 272 273 274 275 276 277 278 279 280 281 282 283 284 285 286 287 288 289 290 291
@itemize @bullet

@item
We are using @uref{http://www.bitkeeper.com/, BitKeeper} for source management.

@item
You should use the @strong{MySQL} 3.23 or 4.0 source for all developments.

@item
If you have any questions about the @strong{MySQL} source, you can post these
to @email{developers@@mysql.com} and we will answer them.
Note that we will shortly change the name of this list to
@email{internals@@mysql.com}, to more accurately reflect what should be
posted to this list.

@item
Try to write code in a lot of black boxes that can be reused or at
least have a clean interface.

@item
Reuse code;  There is already a lot of algorithms in MySQL for list handling,
queues, dynamic and hashed arrays, sorting, etc. that can be reused.

@item
Try to always write optimized code, so that you don't have to
go back and rewrite it a couple of months later.  It's better to
spend 3 times as much time designing and writing an optimal function than
having to do it all over again later on.

@item
Avoid CPU wasteful code, even where it does not matter, so that
you will not develop sloppy coding habits.

@item
If you can write it in fewer lines, do it (as long as the code will not
be slower or much harder to read).

@item
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 easier to read.

@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''.

@item
Use the @code{my_*} functions like @code{my_read()}/@code{my_write()}/
@code{my_malloc()} that you can find in the @code{mysys} library instead 
of the direct system calls;  This will make your code easier to debug and 
more portable.

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

@item
Avoid using @code{malloc()} (its REAL slow);  For memory allocations 
that only need to live for the lifetime of one thread, one should use
@code{sql_alloc()} instead.

@item
Before making big design decisions, please first post a summary of
what you want to do, why you want to do it, and how you plan to do
it.  This way we can easily provide you with feedback and also
easily discuss it thoroughly if some other developer thinks there is better
way to do the same thing!

@item
Use my_var as opposed to myVar or MyVar (@samp{_} rather than dancing SHIFT
to seperate words in identifiers).

@item
Class names start with a capital letter.

@item
Structure types are @code{typedef}'ed to an all-caps identifier.

@item
Any @code{#define}'s are in all-caps.

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

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

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

@item
Using @code{goto} is okay if not abused.

@item
Avoid default variable initalizations, use @code{LINT_INIT()} if the
compiler complains after making sure that there is really no way
the variable can be used uninitialized.

@item
Do not instantiate a class if you do not have to.

@item
Use pointers rather than array indexing when operating on strings.

@end itemize

292
@node mysys functions,,,
293 294 295 296 297 298 299 300 301 302 303 304 305 306 307 308 309 310 311 312 313 314 315 316 317 318 319 320 321 322 323 324 325 326 327 328 329 330 331 332 333 334 335 336 337 338 339 340 341 342 343 344 345 346 347 348 349 350 351 352 353 354 355 356 357 358 359 360 361 362 363 364 365 366 367 368 369 370 371 372 373 374 375 376 377 378 379 380 381 382 383 384 385 386 387 388 389 390 391 392 393 394 395 396 397 398 399 400 401 402 403 404 405 406 407 408 409 410 411 412 413 414 415 416 417 418 419 420 421 422 423 424 425 426 427 428 429 430 431 432 433 434 435
@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));
	format a filename with replace of library and extension and
	converts between different systems.
	params to and name may be identicall
	function dosn't change name if name != to
	Flag may be:	1   force replace filnames library with 'dsk'
			2   force replace extension with 'form' */
			4   force Unpack filename (replace ~ with home)
			8   Pack filename as short as possibly for output to
			    user.
	All open requests should allways use at least:
	"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.

 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.

 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
	  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

 void end_key_cache _A((void));
	- End key-cacheing.

436 437 438 439 440 441 442 443 444 445 446 447 448 449 450 451 452 453 454 455 456 457 458 459 460 461 462 463 464 465 466 467 468 469 470 471 472 473 474 475 476 477 478 479 480 481 482 483 484 485 486 487 488 489 490 491 492 493 494 495 496 497 498 499 500 501 502 503 504 505 506 507 508 509 510 511 512 513 514 515 516 517 518 519 520 521 522 523 524 525 526 527 528 529 530 531 532 533 534 535 536 537 538 539 540 541 542 543 544 545 546 547 548 549 550 551 552 553 554 555 556 557 558 559 560 561 562 563 564 565 566 567 568 569 570 571 572 573 574 575 576 577 578 579 580 581 582 583 584 585 586 587 588 589 590 591 592 593 594 595 596 597 598 599 600 601 602 603 604 605 606 607 608 609 610 611 612 613 614 615 616 617 618 619 620 621 622 623 624 625 626 627 628 629 630 631 632 633 634
@node protocol,,,
@chapter MySQL client/server protocol

Raw packet without compression
============================== 	
-------------------------------------------------
| Packet Length	| Packet no 	| Data		|
| 3 Bytes	| 1 Byte 	| n Bytes	|
-------------------------------------------------

3 Byte packet length
  The length is calculated with int3store
  See include/global.h for details.
  The max packetsize can be 16 MB.
1 Byte packet no

If no compression is used the first 4 bytes of each paket
is the header of the paket.
The packet number is incremented for each sent packet. The first
packet starts with 0		

n Byte data 

The packet length can be recalculated with:
length = byte1 + (256 * byte2) + (256 * 256 * byte3)
		
Raw packet with compression
=========================== 	
-----------------------------------------------------
| Packet Length	| Packet no | Uncomp. Packet Length |
| 3 Bytes	| 1 Byte    | 3 Bytes		    |
-----------------------------------------------------

3 Byte packet length
  The length is calculated with int3store
  See include/global.h for details.
  The max packetsize can be 16 MB.
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.
		
Basic packets
==============
OK-packet	
	For details see sql/net_pkg.cc
	function send_ok
	-------------------------------------------------
	| Header	| No of Rows 	| Affected Rows |
	| 		| 1 Byte 	| 1-8 Byte	|
	-------------------------------------------------
	| ID (last_insert_id)	| Status | Length 	|
	| 1-8 Byte		| 2 Byte | 1-8 Byte	|
	-------------------------------------------------
	| Messagetext					|
	| n Byte					|
	-------------------------------------------------

	Header
	1 byte number of rows ? (always 0 ?)
	1-8 bytes affected rows
	1-8 byte id (last_insert_id) 
	2 byte Status (usually 0)
	If the OK-packege includes a message:
	1-8 bytes length of message
	n bytes messagetext

Error-packet	
	-------------------------------------------------
	| Header	| Statuscode	| Error no	|
	| 		| 1 Byte 	| 2 Byte	|
	-------------------------------------------------
	| Messagetext			       | 0x00	|
	| n Byte			       | 1 Byte |
	-------------------------------------------------
	
	Header
	1 byte status code (0xFF = ERROR)
	2 byte error number (is only sent to new 3.23 clients.
	n byte errortext
	1 byte 0x00



The communication
=================

> Packet from server to client
< Paket from client tor server

	Login
	------
		> 1. packet	
		Header
		1 byte protocolversion
		n byte serverversion
		1 byte 0x00
		4 byte threadnumber 
		8 byte crypt seed 
		1 byte 0x00
		2 byte CLIENT_xxx options (see include/mysql_com.h
			that is supported by the server
		1 byte number of current server charset
		2 byte server status variables (SERVER_STATUS_xxx flags)
		13 byte 0x00 (not used yet).

		< 2. packet	
		Header
		2 byte CLIENT_xxx options
		3 byte max_allowed_packet for the client
		n byte username
		1 byte 0x00
		8 byte crypted password
		1 byte 0x00
		n byte databasename
		1 byte 0x00 

		> 3. packet	
		OK-packet


	Command
	--------
		< 1. packet	
		Header
		1 byte command type (e.g.0x03 = query)
		n byte query

	Result set (after command)
	--------------------------
		> 2. packet	
		Header
		1-8 byte field_count (packed with net_store_length())
		
		If field_count == 0 (command): 
		1-8 byte affected rows
		1-8 byte insert id
		2 bytes server_status (SERVER_STATUS_xx) 		
		
		If field_count == NULL_LENGTH (251)
		LOAD DATA LOCAL INFILE

		If field_count > 0 Result Set:

		> n packets	
		Header Info
		Column description: 5 data object /column
		(See code in unpack_fields())
		
		Columninfo for each column:
			1 data block table_name
			    1 byte length of block
			    n byte data
			1 data block field_name
			    1 byte length of block...
			    n byte data
			1 data block display length of field
			    1 byte length of block
			    3 bytes display length of filed
			1 data block type field of type (enum_field_types)
			    1 byte length of block
			    1 bytexs field of type
			1 data block flags
			    1 byte length of block
			    2 byte flags for the columns (NOT_NULL_FLAG, ZEROFILL_FLAG....)
			    1 byte decimals

		if table definition:
			1 data block default value

		Actual result (one packet per row):
		4 byte header
		1-8 byte length of data
		n data
		
 
Fieldtype Codes:
================

		display_length 	|enum_field_type	|flags
		----------------------------------------------------
Blob		03 FF FF 00	|01 FC			|03 90 00 00
Mediumblob	03 FF FF FF	|01 FC			|03 90 00 00
Tinyblob	03 FF 00 00	|01 FC			|03 90 00 00
Text		03 FF FF 00	|01 FC			|03 10 00 00
Mediumtext	03 FF FF FF	|01 FC			|03 10 00 00
Tinytext	03 FF 00 00	|01 FC			|03 10 00 00
Integer		03 0B 00 00	|01 03			|03 03 42 00
Mediumint	03 09 00 00 	|01 09			|03 00 00 00
Smallint	03 06 00 00	|01 02			|03 00 00 00
Tinyint		03 04 00 00	|01 01			|03 00 00 00
Varchar		03 XX 00 00	|01 FD			|03 00 00 00
Enum		03 05 00 00	|01 FE			|03 00 01 00
Datetime	03 13 00 00	|01 0C			|03 00 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

635

636 637 638 639 640 641
@c The Index was empty, and ugly, so I removed it. (jcole, Sep 7, 2000)

@c @node Index
@c @unnumbered Index

@c @printindex fn
bk@work.mysql.com's avatar
bk@work.mysql.com committed
642 643 644 645 646

@summarycontents
@contents

@bye