Cache SHA1 digest result?
I'm storing several versions of a file based on a digest of the original filename and its version, like this:
$filename = sha1($original . ':' . $version);
Would it be worth it to cache the digest ($filename) in memcache as a key/valu开发者_运维问答e pair (the key being the original + version and value the sha1 hash), or is generating the digest quick enough (for a high traffic php web app)?
Thanks,
Johnathan
You're much better off not caching the hashes. Computing 100,000 hashes on short filenames takes around 1/2 a second on my laptop (a reasonably fast Core 2 Duo):
byte[][] fileNames = Enumerable.Range(0, 100).Select(i => new UnicodeEncoding().GetBytes(System.IO.Path.GetRandomFileName())).ToArray();
Stopwatch stopWatch = new Stopwatch();
using (SHA1CryptoServiceProvider sha1 = new SHA1CryptoServiceProvider())
{
stopWatch.Start();
for (int j = 0; j < 1000; j++)
{
for (int i = 0; i < 100; i++)
{
sha1.ComputeHash(fileNames[i]);
}
}
stopWatch.Stop();
Console.WriteLine("Total: {0}", stopWatch.Elapsed);
Console.WriteLine("Time per hash: {0}", new TimeSpan(stopWatch.ElapsedTicks / 100000));
}
Total: 00:00:00.5186110 Time per hash: 00:00:00.0000014
Hashes are extremely fast, especially for small inputs (such as the name and version of a file).
Now, if you were hashing the files themselves, and they were very large, that would be a different story (simply because it would take so long to read the entire file from off the disk)
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