Re: [Ruby-DBI-devel] is select_all lazy?

[Paul D. <pa...@sn...>]

At 16:21 -0400 7/30/03, Steven Richman wrote:
>Hi,
>
>I'm using DBI with MySQL, and am having a problem using the block version
>of select_all with a large table.
>
>If I do
>     dbh.select_all('select * from small_table') do |row|
>       p row
>     end
>it works fine.
>
>If I do
>     dbh.select_all('select * from big_table limit 10') do |row|
>       p row
>     end
>it works fine.
>
>If I do
>     dbh.select_all('select * from big_table') do |row|
>       p row
>     end
>(where big_table is 25 gigs) it hangs without executing the block, and
>the mysqld server process pegs the CPU.
>
>I'm guessing that the block version of select_all is fetching the entire
>result set instead of fetching rows lazily (i.e., it's equivalent to
>dbh.select_all(...).each do |row|). Please tell me this isn't the case...

It's the case.  The MySQL driver for DBI (dbd_mysql) operates in
such a way that the mysql_store_result() from the C library is
used in all cases, rather than mysql_use_result().

>
>thanks a lot,
>steven.