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* ecpg: how select/insert n rows (array) in one query
@ 2000-06-10 14:49 Jorma O. Tähtinen <jotahtin@alpha.hut.fi>
0 siblings, 1 reply; 2+ messages in thread
From: Jorma O. Tähtinen @ 2000-06-10 14:49 UTC (permalink / raw)
To: pgsql-interfaces
Hello
I'm new postgres user (currenly converting db application with quite
large database from mysql to postgres, hopefully pg is not too slow but
I really need triggers and views).
Anyway could somebody please explain how multiple row select/insert
should be used in embedded sql (ecpg)
1) select - this is simple (well documented)
EXEC SQL BEGIN DECLARE SECTION;
struct data_t {
char md5[100][32];
int size[100];
} data;
struct ind_t { short md5,size } ind;
EXEC SQL END DECLARE SECTION;
EXEC SQL BEGIN TRANSACTION;
EXEC SQL DECLARE cur CURSOR FOR
select md5,size FROM filetable;
EXEC SQL OPEN cur;
EXEC SQL WHENEVER NOT FOUND DO break;
while(1) {
EXEC SQL FETCH 1000 FROM cur INTO :data:ind;
for(n=0;n<sqlca.sqlerrd[2];++n) { /*do something*/
}
EXEC SQL CLOSE cur;
EXEC SQL COMMIT;
This is fine, speed on my hardware about (magnitude) 10.000 rows/per
sec.
(mostly limited by disk i/o)
Only question here is: why can't I declare that data struct like
struct data_t {
char md5[32];
int size;
} data[100];
Is this possible and how to use it.
.
2) insert - Now this is my real problem
if I have understod docs correctly : use of insert like select in
about example is NOT possible
please somebody say that I'm wrong - small example would be nice to
see ;-)
And yes I have tried to insert multiple rows in one transaction
block like
EXEC SQL BEGIN TRANSACTION
for(....) {
insert .....
}
EXEC SQL COMMIT
but this is still way to slow at max 50-100 insert per sec. I
understand that inserting is slow operation
but 10.000/sec in select and 50/sec in insert - can't be THAT
slow??? (inserting 12-13M rows is a bit pain...;-)
And yes, I really want to use c+embedded sql code to do inserting
(real app/table struct of course more complex)
-jt-
^ permalink raw reply [nested|flat] 2+ messages in thread
* Re: ecpg: how select/insert n rows (array) in one query
@ 2000-06-14 15:21 Michael Meskes <meskes@postgresql.org>
parent: Jorma O. Tähtinen <jotahtin@alpha.hut.fi>
0 siblings, 0 replies; 2+ messages in thread
From: Michael Meskes @ 2000-06-14 15:21 UTC (permalink / raw)
To: Jorma O. Tähtinen <jotahtin@alpha.hut.fi>; +Cc: pgsql-interfaces
On Sat, Jun 10, 2000 at 05:49:42PM +0300, Jorma O. Tähtinen wrote:
> 1) select - this is simple (well documented)
> ...
> EXEC SQL BEGIN DECLARE SECTION;
> struct data_t {
> char md5[100][32];
> int size[100];
> } data;
> ...
> Only question here is: why can't I declare that data struct like
> struct data_t {
> char md5[32];
> int size;
> } data[100];
> Is this possible and how to use it.
Hmm, it certainly should be possible. I will look into it as soon as I find
some spare time. I do not remember if there was a real problem with this.
> if I have understod docs correctly : use of insert like select in
> about example is NOT possible
> please somebody say that I'm wrong - small example would be nice to
> see ;-)
selects work because the backend returns more than one tuple at a time.
However, inserts do not work that way. An SQL insert command is designed to
insert one tuple. I wouldn't know which syntax to use to do that sort of
bulk loading.
> And yes I have tried to insert multiple rows in one transaction
> block like
> EXEC SQL BEGIN TRANSACTION
> for(....) {
> insert .....
> }
> EXEC SQL COMMIT
>
> but this is still way to slow at max 50-100 insert per sec. I
> understand that inserting is slow operation
Try starting the backend without -F and putting each insert into its own
transaction. Keeping lots of updates/insert in one transaction always slows
down a system. The very same would happen to mysql if it used transactions.
> And yes, I really want to use c+embedded sql code to do inserting
> (real app/table struct of course more complex)
If this is a ecpg problem we surely will fix it. But I doubt the performance
is better when using psql to enter the data.
Michael
--
Michael Meskes
Michael@Fam-Meskes.De
Go SF 49ers! Go Rhein Fire!
Use Debian GNU/Linux! Use PostgreSQL!
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2000-06-10 14:49 ecpg: how select/insert n rows (array) in one query Jorma O. Tähtinen <jotahtin@alpha.hut.fi>
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