maria-developers team mailing list archive

[Shubham Barai <shubhambaraiss@xxxxxxxxx>]

Hi Sergei,
           Sorry! I made a mistake. Actually, when I changed my storage
engine to MyISAM and executed  create table statement(with unique blobs and
no prefix length),mysqld crashed. After reconnecting to the server, the
storage engine got changed to default (InnoDB).I didn't know about that and
I executed all queries on InnoDB. I thought my patch was working for MyISAM
but there are some issues.I am working on it but it might require some time
to get it working. Since application deadline for GSoC is 25 March, I will
try to submit my proposal as early as possible.

Thanks,
Shubham

On 19 March 2016 at 14:22, Shubham Barai <shubhambaraiss@xxxxxxxxx> wrote:

> Hello Sergei,
>
>             As you suggested, I tried  to develop a prototype  just for
> blobs.
> So far it is working fine but I am still verifying  it for different
>  cases.
> I will provide you the link to my Github repository shortly.
>
> Thanks,
> Shubham
>
> On 16 March 2016 at 17:55, Sergei Golubchik <serg@xxxxxxxxxxx> wrote:
>
>> Hi, Shubham!
>>
>> On Mar 16, Shubham Barai wrote:
>> > Hello, Sergie!
>> >  I  tried to explore the source code from
>> > mi_create.c,ha_myisam.cc,sql/sql_table.cc,include/myisam.h,.and some
>> other
>> > files.
>> > The main task is to create  MI_UNIQUEDEF "uniques" for long unique
>> > constraints.
>> > We have to consider all the cases where we need to create MI_UNIQUEDEF
>> > instead of MI_KEYDEF.
>> >
>> > It will include queries like
>> >            create table table1 (blob_column blob,unique(blob_column) );
>> >            create table table1 (a int,blob_column
>> > blob,unique(a,blob_column) );
>> >            create table table1 (a int,blob_column1 blob,blob_column2
>> > blob,unique(blob_column1(300),blob_column2) );
>> > (key with multiple blob columns and one of the blob column specified
>> with
>> > prefix length).
>> >
>> > I think we have to create  MI_UNIQUEDEF if any one of the columns in a
>> key
>> > is a blob field without  prefix length.
>>
>> Yes. And also for any other UNIQUE constraint that is too long for a
>> normal index. For example, many long VARCHAR columns.
>>
>> But, of course, for a prototype one can start just with blobs.
>>
>> > In sql/sql_table, mysql_prepare_create_table is the function which
>> > prepares the table and key structures for table creation in mi_create.
>> > It generates an error if any one of the blob fields in a key is
>> > specified without length.  Currently, this task is limited to MyISAM,
>> > so if any other storage engine is selected, we have to generate the
>> > same error in mysql_prepare_create_table.
>>
>> There's a generic check whether the key is too long. It can be used
>> here, it doesn't depend on the storage engine.
>>
>> > In storage/myisam/ha_myisam.cc, table2myisam is a function which
>> allocates
>> > and initializes myisam key and column definitions.The current function
>> > prototype of table2myisam is
>> >        table2myisam(TABLE  *table_arg, MI_KEYDEF  **keydef_out,
>> > MI_COLUMNDEF **recinfo_out, uint records_out)
>> > We have to change it to
>> >    table2myisam(TABLE  *table_arg,MI_KEYDEF  **keydef_out,MI_UNIQUEDEF
>> **
>> > uniquedef_out,MI_COLUMNDEF  **recinfo_out,uint records_out)
>>
>> Right.
>>
>> > table2myisam initializes all the key definitions from
>> table_arg->keyinfo.
>> > So we can  set  a new flag  (say uniquedef) in a keyinfo struct in
>> > mysql_prepare_create_table if any one of the key_part consists of blob
>> > field without prefix length.
>>
>> There's a field 'algorithm' already. Because MI_UNIQUEDEF in MyISAM is,
>> basically, an index of hashed column values, it is kind of a hash index.
>> So you can use algorithm=HA_KEY_ALG_HASH to mark such columns. And the
>> user will be able to create these indexes explicitly with
>>
>>   create table table1 (blob_column blob,unique(blob_column) using hash);
>>
>> > Later we can check the flag in table2myisam to see  if we want to
>> > create MI_KEYDEF or MI_UNIQUEDEF.
>> >
>> > Thanks,
>> > Shubham.
>>
>> Very good!
>>
>> Regards,
>> Sergei
>> Chief Architect MariaDB
>> and security@xxxxxxxxxxx
>>
>
>