Memcache key generation strategy
- by Maxim Veksler
Given function f1 which receives n String arguments, would be considered better random key generation strategy for memcache for the scenario described below ?
Our Memcache client does internal md5sum hashing on the keys it gets
public class MemcacheClient {
public Object get(String key) {
String md5 = Md5sum.md5(key)
// Talk to memcached to get the Serialization...
return memcached(md5);
}
}
First option
public static String f1(String s1, String s2, String s3, String s4) {
String key = s1 + s2 + s3 + s4;
return get(key);
}
Second option
/**
* Calculate hash from Strings
*
* @param objects vararg list of String's
*
* @return calculated md5sum hash
*/
public static String stringHash(Object... strings) {
if(strings == null)
throw new NullPointerException("D'oh! Can't calculate hash for null");
MD5 md5sum = new MD5();
// if(prevHash != null)
// md5sum.Update(prevHash);
for(int i = 0; i < strings.length; i++) {
if(strings[i] != null) {
md5sum.Update("_" + strings[i] + "_"); // Convert to String...
} else {
// If object is null, allow minimum entropy by hashing it's position
md5sum.Update("_" + i + "_");
}
}
return md5sum.asHex();
}
public static String f1(String s1, String s2, String s3, String s4) {
String key = stringHash(s1, s2, s3, s4);
return get(key);
}
Note that the possible problem with the second option is that we are doing second md5sum (in the memcache client) on an already md5sum'ed digest result.
Thanks for reading,
Maxim.
