求mysql 关于blob的接口
BLOB是一个二进制大对象，可以容纳可变数量的数据。有4种BLOB类型：TINYBLOB、BLOB、MEDIUMBLOB和LONGBLOB。它们只是可容纳值的最大长度不同。mysql有些存储引擎是支持blob类型的，有些不支持。例如，MYISAM和falcon都是支持blob的。
我现在的问题是，mysql是如何调用函数来处理blob这种特殊类型的。例如，在一个含有blob字段的表里面执行update,insert,delete这些操作的时候，函数是如何调用的。
由于MYISAM是大多数表的默认存储引擎，所以我就研究了一下MYISAM。
我看了十多天MYISAM的源代码，始终没有搞明白里面的函数调用关系。因为结构太复杂了！在mysql-6.0.3/storage/myisam/目录下有个Mi_update.c文件，代码如下：
/* Update an old row in a MyISAM table */
#include "fulltext.h"
#include "rt_index.h"
int mi_update(register MI_INFO *info, const uchar *oldrec, uchar *newrec)
{//MI_INFO在myisamdef.h定义
int flag,key_changed,save_errno;
reg3 my_off_t pos;
uint i;
uchar old_key,*new_key;//#define MI_MAX_KEY_BUFF(MI_MAX_KEY_LENGTH+MI_MAX_KEY_SEG*6+8+8)
bool auto_key_changed=0;
ulonglong changed;
MYISAM_SHARE *share=info->s;
ha_checksum old_checksum;
DBUG_ENTER("mi_update");
LINT_INIT(new_key);
LINT_INIT(changed);
LINT_INIT(old_checksum);
DBUG_EXECUTE_IF("myisam_pretend_crashed_table_on_usage",
mi_print_error(info->s, HA_ERR_CRASHED);
DBUG_RETURN(my_errno= HA_ERR_CRASHED););
if (!(info->update & HA_STATE_AKTIV))
{
DBUG_RETURN(my_errno=HA_ERR_KEY_NOT_FOUND);
}
if (share->options & HA_OPTION_READ_ONLY_DATA)
{
DBUG_RETURN(my_errno=EACCES);
}
if (info->state->key_file_length >= share->base.margin_key_file_length)
{
DBUG_RETURN(my_errno=HA_ERR_INDEX_FILE_FULL);
}
pos=info->lastpos;
if (_mi_readinfo(info,F_WRLCK,1))
DBUG_RETURN(my_errno);
if (share->calc_checksum)
old_checksum=info->checksum=(*share->calc_checksum)(info,oldrec);
if ((*share->compare_record)(info,oldrec))
{
save_errno=my_errno;
goto err_end; /* Record has changed */
}
/* Calculate and check all unique constraints */
key_changed=0;
for (i=0 ; i < share->state.header.uniques ; i++)
{
MI_UNIQUEDEF *def=share->uniqueinfo+i;
if (mi_unique_comp(def, newrec, oldrec,1) &&
mi_check_unique(info, def, newrec, mi_unique_hash(def, newrec),
info->lastpos))
{
save_errno=my_errno;
goto err_end;
}
}
if (_mi_mark_file_changed(info))
{
save_errno=my_errno;
goto err_end;
}
/* Check which keys changed from the original row */
new_key=info->lastkey2;
changed=0;
for (i=0 ; i < share->base.keys ; i++)
{
if (mi_is_key_active(share->state.key_map, i))
{
if (share->keyinfo.flag & HA_FULLTEXT )//128
{
if (_mi_ft_cmp(info,i,oldrec, newrec))//ft_update.c
{
if ((int) i == info->lastinx)
{
/*
We are changeing the index we are reading on.Mark that
the index data has changed and we need to do a full search
when doing read-next
*/
key_changed|=HA_STATE_WRITTEN;//4//4
}
changed|=((ulonglong) 1 << i);
if (_mi_ft_update(info,i, old_key,oldrec,newrec,pos))
goto err;
}
}
else
{
uint new_length=_mi_make_key(info,i,new_key,newrec,pos);//Mi_key.c
uint old_length=_mi_make_key(info,i,old_key,oldrec,pos);
/* The above changed info->lastkey2. Inform mi_rnext_same(). */
info->update&= ~HA_STATE_RNEXT_SAME; //4096
if (new_length != old_length ||
memcmp((uchar*) old_key,(uchar*) new_key,new_length))
{
if ((int) i == info->lastinx)
key_changed|=HA_STATE_WRITTEN; /* Mark that keyfile changed */
changed|=((ulonglong) 1 << i);
share->keyinfo.version++;
if (share->keyinfo.ck_delete(info,i,old_key,old_length)) goto err;
if (share->keyinfo.ck_insert(info,i,new_key,new_length)) goto err;
if (share->base.auto_key == i+1)
auto_key_changed=1;
}
}
}
}
/*
If we are running with external locking, we must update the index file
that something has changed.
*/
if (changed || !my_disable_locking)
key_changed|= HA_STATE_CHANGED;// 1 database has changed
if (share->calc_checksum)
{
info->checksum=(*share->calc_checksum)(info,newrec);
/* Store new checksum in index file header */
key_changed|= HA_STATE_CHANGED;
}
{
/*
Don't update index file if data file is not extended and no status
information changed
*/
MI_STATUS_INFO state; // st_mi_status_info Myisamdef.h
ha_rows org_split;
my_off_t org_delete_link;
memcpy((char*) &state, (char*) info->state, sizeof(state));
org_split= share->state.split;
org_delete_link= share->state.dellink;
if ((*share->update_record)(info,pos,newrec))
goto err;
if (!key_changed &&
(memcmp((char*) &state, (char*) info->state, sizeof(state)) ||
org_split != share->state.split ||
org_delete_link != share->state.dellink))
key_changed|= HA_STATE_CHANGED;/* Must update index file */
}
if (auto_key_changed)
set_if_bigger(info->s->state.auto_increment,
retrieve_auto_increment(info, newrec));
if (share->calc_checksum)
info->state->checksum+=(info->checksum - old_checksum);
info->update= (HA_STATE_CHANGED | HA_STATE_ROW_CHANGED | HA_STATE_AKTIV |
key_changed);
myisam_log_record(MI_LOG_UPDATE,info,newrec,info->lastpos,0);
/*
Every myisam function that updates myisam table must end with
call to _mi_writeinfo(). If operation (second param of
_mi_writeinfo()) is not 0 it sets share->changed to 1, that is
flags that data has changed. If operation is 0, this function
equals to no-op in this case.
mi_update() must always pass !0 value as operation, since even if
there is no index change there could be data change.
*/
VOID(_mi_writeinfo(info, WRITEINFO_UPDATE_KEYFILE));
allow_break(); /* Allow SIGHUP & SIGINT */
if (info->invalidator != 0)
{
DBUG_PRINT("info", ("invalidator... '%s' (update)", info->filename));
(*info->invalidator)(info->filename);
info->invalidator=0;
}
DBUG_RETURN(0);
err:
DBUG_PRINT("error",("key: %derrno: %d",i,my_errno));
save_errno=my_errno;
if (changed)
key_changed|= HA_STATE_CHANGED;
if (my_errno == HA_ERR_FOUND_DUPP_KEY || my_errno == HA_ERR_OUT_OF_MEM ||
my_errno == HA_ERR_RECORD_FILE_FULL)
{
info->errkey= (int) i;
flag=0;
do
{
if (((ulonglong) 1 << i) & changed)
{
if (share->keyinfo.flag & HA_FULLTEXT)
{
if ((flag++ && _mi_ft_del(info,i, new_key,newrec,pos)) ||
_mi_ft_add(info,i, old_key,oldrec,pos))
break;
}
else
{
uint new_length=_mi_make_key(info,i,new_key,newrec,pos);
uint old_length= _mi_make_key(info,i,old_key,oldrec,pos);
if ((flag++ && _mi_ck_delete(info,i,new_key,new_length)) ||
_mi_ck_write(info,i,old_key,old_length))
break;
}
}
} while (i-- != 0);
}
else
{
mi_print_error(info->s, HA_ERR_CRASHED);
mi_mark_crashed(info);
}
info->update= (HA_STATE_CHANGED | HA_STATE_AKTIV | HA_STATE_ROW_CHANGED |
key_changed);
err_end:
myisam_log_record(MI_LOG_UPDATE,info,newrec,info->lastpos,my_errno);
VOID(_mi_writeinfo(info,WRITEINFO_UPDATE_KEYFILE));
allow_break(); /* Allow SIGHUP & SIGINT */
if (save_errno == HA_ERR_KEY_NOT_FOUND)
{
mi_print_error(info->s, HA_ERR_CRASHED);
save_errno=HA_ERR_CRASHED;
}
DBUG_RETURN(my_errno=save_errno);
} /* mi_update */
看代码没有blob这个单词，而是通过调用了一些其他函数，例如：_mi_ft_update：
/* update a document entry */
int _mi_ft_update(MI_INFO *info, uint keynr, uchar *keybuf,
const uchar *oldrec, const uchar *newrec, my_off_t pos)
{
int error= -1;
FT_WORD *oldlist,*newlist, *old_word, *new_word;
CHARSET_INFO *cs=info->s->keyinfo.seg->charset;
uint key_length;
int cmp, cmp2;
DBUG_ENTER("_mi_ft_update");
if (!(old_word=oldlist=_mi_ft_parserecord(info, keynr, oldrec,
&info->ft_memroot)) ||
!(new_word=newlist=_mi_ft_parserecord(info, keynr, newrec,
&info->ft_memroot)))
goto err;
error=0;
while(old_word->pos && new_word->pos)
{
cmp= mi_compare_text(cs, (uchar*) old_word->pos,old_word->len,
(uchar*) new_word->pos,new_word->len,0,0);
cmp2= cmp ? 0 : (fabs(old_word->weight - new_word->weight) > 1.e-5);
if (cmp < 0 || cmp2)
{
key_length=_ft_make_key(info,keynr,keybuf,old_word,pos);
if ((error=_mi_ck_delete(info,keynr,(uchar*) keybuf,key_length)))
goto err;
}
if (cmp > 0 || cmp2)
{
key_length=_ft_make_key(info,keynr,keybuf,new_word,pos);
if ((error=_mi_ck_write(info,keynr,(uchar*) keybuf,key_length)))
goto err;
}
if (cmp<=0) old_word++;
if (cmp>=0) new_word++;
}
if (old_word->pos)
error=_mi_ft_erase(info,keynr,keybuf,old_word,pos);
else if (new_word->pos)
error=_mi_ft_store(info,keynr,keybuf,new_word,pos);
err:
free_root(&info->ft_memroot, MYF(MY_MARK_BLOCKS_FREE));
DBUG_RETURN(error);
}
还有很多其他代码！
我们项目小组想写一个支持blob操作的存储引擎，不过我是个菜鸟。希望各位大侠出手相助！
这些函数究竟是怎样调用的呢？可以说一下某种引擎（如myisam）的某个操作（如update,write_row,delete)。当然讲得越多越详细越好！
谢谢！
[ 本帖最后由 oken 于 2008-8-15 18:38 编辑 ]
页:
[1]