maria-developers team mailing list archive

["Berrocal, Eduardo" <eduardo.berrocal@xxxxxxxxx>]

Hello Sergei,

Thanks a lot for your response. 

I have tried to use that route but without success. The problem is that I can only access the last record read from table1. 

Let say that, during the JOIN, 3 rows are read from table1. These 3 rows will be compared against all rows from table2. I want to avoid a full scan of table2 by passing the value for the field from those 3 rows down to the storage engine. When condition pushdown is called on table2, and I try to access those 3 rows, I can only access the last one read through f1->field->ptr (or f1->table->record[0]).

For what I understand, f1->table does not store an array of read records during JOIN. Am I right? That is stored in the JOIN_CACHE object. Please correct me if I am wrong here.

Thanks again for your help,


Eduardo Berrocal García de Carellán
Senior Software Engineer


Intel Corporation  |  intel.com


-----Original Message-----
From: Sergei Golubchik <serg@xxxxxxxxxxx> 
Sent: Thursday, July 8, 2021 12:43 AM
To: Berrocal, Eduardo <eduardo.berrocal@xxxxxxxxx>
Cc: maria-developers@xxxxxxxxxxxxxxxxxxx
Subject: Re: [Maria-developers] Accessing read records during join for condition pushdown

Hi, Berrocal,!

On Jul 06, Berrocal, Eduardo wrote:
> Hello list (first email here, hopefully sending it to the right 
> address), I have been trying to solve this problem for a while now, 
> and I am stuck. I wonder if what I am trying to do is even possible.
> 
> I am implementing a new storage engine which handles engine condition 
> pushdown. Now, when MariaDB is working on a JOIN using more than one 
> table (for simplicity, let's assume 2), how can I access the read 
> records for table 1 when working on a condition pushdown for table 2?
> When joining like this: table1.field1 = table2.field1, I can see 2 
> Item objects of type FIELD in the condition. However, I can't find 
> where the read records for table1 are so I can effectively filter 
> records in table2 by those values.

if f1 is Item_field for table1.field1, then generally

  f1->field->table->record[0]

is the current record for the table1, and

  f1->field->ptr

is the pointer to the field1 value in that currect record

> Thanks a lot for your help,
> 
> Eduardo Berrocal García de Carellán
> Senior Software Engineer
> Intel Corporation  |  intel.com<http://intel.com/>

Regards,
Sergei
VP of MariaDB Server Engineering
and security@xxxxxxxxxxx