Hi Sergei!
Actually I completed the work on update and delete. Now they will use index for looking up records.
But I am thinking I have done a lot of changes in optimizer which may break it , and also there are lots of queries where my
code does not work, fixing this might take a long amount of time.
I am thinking of a change in my existing code :-
Suppose a table t1
create table t1 (a blob, b blob, c blob, unique(a,b,c));
In current code , for query like there will a KEY with only one keypart which points to field DB_ROW_HASH_1.
It was okay for normal updates , insert and delete , but in the case of where optimization I have do a lot of stuff , first to match field (like in add_key_part), then see whether all the fields in hash_str are present in where or not, then create keys by calculating hash. I do this by checking the HA_UNIQUE_HASH flag in KEY , but this also makes (I think) optimizer code
bad because of too much dependence. Also I need to patch get_mm_parts and get_mm_leaf function , which I think
should not be patched.
I am thinking of a another approach to this problem at server level instead of having just one keypart we can have 1+3
keypart. Last three keypart will be for field a, b, c and first one for DB_ROW_HASH_1 .These will be only at server level not at
storage level. key_info->key_part will point at keypart containing field a , while key_part having field DB_ROW_HASH_1 will
-1 index. By this way I do not have to patch more of optimizer code. But there is one problem , what should be the length of
key_part? I am thinking of it equal to field->pack_length(), this would not work because while creating keys optimizer
calls get_key_image() (which is real data so can exceed pack_lenght() in case of blob), so to get this work I have to patch
optimizer where it calls get_key_image() and see if key is HA_UNIQUE_HASH . If yes then instead of get_key_image just use
memcpy(key, field->ptr(), field->pack_length());
this wont copy the actual data, but we do not need actual data. I will patch handler methods like ha_index_read, ha_index_idx_read , multi_range_read_info_const basically handler methods which are related to index or range search.
In these methods i need to calculate hash , which I can calculate from key_ptr but key_ptr doe not have actual data(in case
of blobs etc).So to get the date for hash , I will make a field clone of (a,b,c etc) but there ptr will point in key_ptr. Then
field->val_str() method will work simply and i can calculate hash. And also I can compare returned result with actual key in
handler method itself.
What do you think of this approach ?
Regards
sachin