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Hack 99 Cache Auction Data to Improve API Efficiency
Reduce the number of API calls your programmakes and work within your daily API allotment.One of the requirements of
certification, as described in [Hack #82], is that your application or
script does not make more calls or retrieve more data than is
absolutely necessary. This is typically accomplished in any of three
ways:Restricting the result set to a specific date range, as described in
[Hack #85].Download only new entries by comparing the current total of entries
with the total you recorded the last time the call was used, as
described in [Hack #96].Caching retrieved data so that it doesn't have to be
retrieved again, as described in this hack.
Which data you cache and how you do it depends on the type of data
you're working with.
8.19.1 Caching Input
Probably the most useful place to start is by recording the item
numbers of all auctions you're currently selling.
Assuming you're using GetItem to
upload your listings to eBay (see [Hack #88]), you can simply save the
resulting item number in a file, like this:
open (OUTFILE,">>$localdir/auctionlist.txt");
print OUTFILE "$rsp->{Item}[0]{Id},$rsp->{Item}[0]{EndTime}\n";
close (OUTFILE);
Eventually, the file will look like this:
4500207651,2005-07-15 20:43:32
4500207783,2005-07-16 08:14:18
4500208002,2005-07-18 19:00:31
with each line containing one item number and one end date, separated
by a comma. Then, instead of using the
GetSellerList API call
found in many hacks in this chapter, you can simply load the list,
like this:
open (INFILE,"$localdir/auctionlist.txt");
my %items = map { split(/,/, $_) } <INFILE>;
close (INFILE);
chomp %items;
which will create a hash of item numbers and end times. To fill an
array with all the item numbers, use the keys
function:
@itemnumbers = keys %items;
To retrieve the end date for a single auction, reference the hash
like this:
$endtime = $items{'4500207783'}Naturally, if you want to store more than just item numbers and end
times, you'll need a more complex storage system,
but the methodology will be the same.Not only will this approach significantly reduce your API usage, it
will end up being a lot faster than repeatedly downloading large
amounts of data from eBay.
8.19.2 Caching Output
Another case where caching can reduce API usage and improve
performance is when it comes to the output your program generates.
For example, the script in [Hack #94]
generates a web page with a listing of your currently running
auctions (with pictures). But instead of generating the same page
every time, you can redirect the output to a static HTML file and
then run the script every so often to generate the file.
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will make it cache its own output. First, add this line immediately
before line [1]:
open (OUTFILE,">/some_directory/galleryl");
where /some_directory is the full path to
the galleryl file. Next, remove line [1] entirely:
print "Content-type: text/html\n\n";
Then, you'll need to convert all print statements in
the script so that their output is redirected to the open file. For
example, change:
print "<html><script type=\"text/javascript\">\n";
to:
print OUTFILE "<html><script type=\"text/javascript\">\n";
Finally, at the end of the script, after line [3], close the file like this:
close (OUTFILE);
That should do it. All that's left to do at this
point is to change the URL in the <iframe>
tag to reflect the address of the static page, like this:
<iframe src="http://www.ebayhacks.com/galleryl"
style="width:100%;margin:0;border:0;">
With this approach, your customers see a cached list of auctions
every time your custom gallery is loaded. Not only will this
eliminate the unnecessary API calls, but the page will load much
faster as well.
