Re: Dealing with a cursor in libpq c program

John Scalia wrote:
> This posting is really two parts and here's part 1. As a test, I've been building text indexes on some
> datasets from our data warehouse. I've built both trigram and gin indexes. My two largest sets threw
> warnings while the gin index was being built of "Cannot index word. Words greater than 2047 characters
> cannot be indexed." Overall, this is not a very helpful message as the two sets contain more than 25
> million rows each. It would have really nice to get a row number or a sample of the errant word with
> the warning message.
>
>
> Part 2 is I'm trying to write a C program to actually find the bad data, and figured that I would use
> a cursor to traverse the table.field and break the field into individual words and test for length. I
> would then output any word over 2000 character long. I cannot find any references however, for using a
> cursor where I only want to process a certain number of rows at a time, say 500. I'm just trying to
> minimize memory as my first attempt at this was an unsuccessful python attempt. I'm testing each
> operation in the c program and see that BEGIN was successful and the cursor declaration was also
> successful.

It would be helpful to know the DECLARE statement...

> Not sure if I need to call an OPEN CURSOR command as no examples I found actually do that and my
> attempt at opening it returns failure. No big deal as I just let the code continue anyway.

You don't OPEN cursors declare with DECLARE.
OPEN is PL/pgSQL only.

Before you write a C program for that, try to run your DECLARE and FETCH statement
from psql. That should give you the same error message with less efort.

> My question is the next step where I want to fetch the next 50 rows, and it's currently failing with
> res = 7. Here's the code fragment which is in a search loop:
>
> res = PQexec(conn, "FETCH FORWARD 500 FROM note_text_cursor");
> printf("res = %d\n", PQresultStatus(res));

7 is PGRES_FATAL_ERROR.

You should call PQerrorMessage(conn) to get the error message.

Yours,
Laurenz Albe