Interesting, I don't have any numerical benchmarks, but I saw a
performance benefit moving my result set into an array.
My case may have been extreme, I was creating a table 350 rows by 350
columns, several megabytes of output, and I found that building the
output directly from the query too slow.
When I moved my results into an array before I started, it moved to a
reasonable build time.
My theory was that I was not getting proper use out of my indexes in my
data set, or that the interface I was using to get to my MS-SQL tables
was inefficient in some other way.
I may not have "proof", but I will be inclined to use this for a
performance boost when working with large sets of data.
On 1/21/2010 6:45 PM, Nathan Rixham wrote:
Shawn McKenzie wrote:
Daevid Vincent wrote:
-----Original Message-----
From: Nathan Rixham [mailto:nrixham@xxxxxxxxx]
you'll also find a performance upgrade if you load all sql
results in to
an array and close up the query / free the results before
working on them.
query
for() {
$results[] = $row;
}
close stuff
work on results
Do you have any proof of this?
What would be the logic here?
Got some example benchmarks?
Got a URL of a whitepaper or something that discusses this?
I would think the only things that the mysql calls are doing is holding
pointers to the next record and DB handle. I can't imagine they are using
that much resources, nor would they be just spinning and waiting tying up
CPU cycles either.
I've never heard this to be the case.
I have proof to the contrary :-)
<?php
echo number_format(memory_get_usage()) . " Bytes used before query\n";
$conn = mysql_connect('localhost', 'x', 'x');
$result = mysql_query("SELECT * FROM table_name");
$count = mysql_num_rows($result);
echo $count . " rows returned\n";
echo number_format(memory_get_usage()) . " Bytes used after query\n";
while($rows[] = mysql_fetch_assoc($result)) { }
echo number_format(memory_get_usage()) . " Bytes used after array
creation\n";
mysql_free_result($result);
echo number_format(memory_get_usage()) . " Bytes used after
mysql_free_result\n";
?>
65,588 Bytes used before query
6940 rows returned
67,264 Bytes used after query
6,376,612 Bytes used after array creation
6,376,756 Bytes used after mysql_free_result
yup appears i was talking bollocks :D lolol - confusion came on my part
from optimisation of a high traffic site over the past few years!
correction:
on simple scripts it is slower, marginally, (due to two for loops and
more data in memory)
however - in real world applications where such nasty practises as
escaping in and out of html to render results and secondary per row
queries or api calls are taken in to account this method of getting
everything out of the db in a single swift action gives the performance
boost - and more over on high traffic sites freeing up the connection /
query resources as quickly as possible makes a rather noticeable impact,
too many open connections and queries can be very nasty when your
getting a few hundred / thousand requests per second.
sorry 'bout that!
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