Casting a Host Structure array into a table - c

Question

I am trying to tune a piece of large code written in Pro*C, specifically a bottleneck loop and an UPDATE statement inside it. The for loop loops through a "Host Structure array" which may contain several thousand at times millions of records and the update executes too many times. The update could be executed more frequently throughout the program but that would need drastic change to the code and I am not in a liberty to make major changes.
So I have something like this
....
#define NULL_REF_NO 10
#define NULL_ERR 256
....
....
struct s_errors
{
char s_ref_id [NULL_REF_NO];
char s_ref_seq_no [NULL_REF_NO];
char s_err_msg [NULL_ERR];
};
....
....
struct s_errors *ps_errors = NULL;
....
....
/*The part below happens throughout the program to collect all errors*/
/*ls_ref_id, ls_ref_seq_no, and ls_err_msg are local variables of same data type. and i_curr_index is the array index variable*/
strcpy(ls_ref_id, ps_errors[i_curr_index].s_ref_id);
strcpy(ls_ref_seq_no, ps_errors[i_curr_index].s_ref_seq_no);
strcpy(ls_err_msg, ps_errors[i_curr_index].s_err_msg);
.....
/* At this point ps_error contains thousands or even millions of rows*/
/* The final part is to update all these rows back to the table like below*/
/* pl_err_count is a Global var which keeps track of the total number of records in the host structure array*/
int i_curr_index = 0;
char l_ref_id [NULL_REF_NO];
char l_ref_seq_no [NULL_REF_NO];
char l_err_msg [NULL_ERR];
for(i_curr_index = 0; i_curr_index < pl_err_count; i_curr_index++)
{
strcpy(l_ref_id, ps_errors[i_curr_index].s_ref_id);
strcpy(l_ref_seq_no, ps_errors[i_curr_index].s_ref_seq_no);
strcpy(l_err_msg, ps_errors[i_curr_index].s_err_msg);
EXEC SQL
UPDATE some_table
SET status = 'E',
error_message = :l_err_msg
WHERE ref_id = :l_ref_id
AND ref_seq_no = :l_ref_seq_no;
if (SQL_ERROR_FOUND)
{
sprintf(err_data, "Updation failed with sql errors ");
strcpy(table, "some_table");
WRITE_ERROR(SQLCODE,function,"",err_data);
return(FATAL);
}
}
The bottleneck is the for loop above (and it's the last step in the program) which loops too many times causing the program to run long. I was wondering if there is a way to CAST the Host Structure array ps_errors to an Oracle table type so that I can easily do bulk UPDATE or even do a MERGE with some parallel DML without having to loop through each and every record.

Answer 1

Extrapolating from some other code I have seen at work which does something sort of similar, you could do something like this instead of the for loop:
EXEC SQL for :pl_err_count
UPDATE some_table
SET status = 'E',
error_message = :ps_errors.s_err_msg
WHERE ref_id = :ps_errors.s_ref_id
AND ref_seq_no = :ps_errors.s_ref_seq_no;
This might rely on the content added to ps_errors being null terminated. Given the use of strcpy() in the existing code rather that strncpy() (or similar), I'm guessing they already are.
If s_err_msg could be null, you should also consider using indicator variables. eg.
error_message = :ps_errors.s_err_msg INDICATOR :indicator_variable

Answer 2

You could use an array update http://docs.oracle.com/cd/B28359_01/appdev.111/b28427/pc_08arr.htm#i1879 but you'll need to change your array of structs ps_errors to be a struct of arrays
E.g:
EXEC SQL
UPDATE some_table
SET status = 'E',
error_message = :ps_errors.s_err_msg
WHERE ref_id = :ps_errors.s_ref_id
AND ref_seq_no = :ps_errors.s_ref_seq_no;