[rhmessaging-commits] rhmessaging commits: r3035 - store/trunk/cpp/lib.

[rhmessaging-commits at lists.jboss.org]

Author: kpvdr
Date: 2009-01-08 09:53:33 -0500 (Thu, 08 Jan 2009)
New Revision: 3035

Modified:
   store/trunk/cpp/lib/MessageStoreImpl.cpp
   store/trunk/cpp/lib/MessageStoreImpl.h
Log:
Improved hash function gives more even distribution of queues across 29 dirs

Modified: store/trunk/cpp/lib/MessageStoreImpl.cpp
===================================================================
--- store/trunk/cpp/lib/MessageStoreImpl.cpp	2009-01-07 20:10:31 UTC (rev 3034)
+++ store/trunk/cpp/lib/MessageStoreImpl.cpp	2009-01-08 14:53:33 UTC (rev 3035)
@@ -1729,15 +1729,20 @@
     return getJrnlDir(queue.getName().c_str());
 }
 
+u_int32_t MessageStoreImpl::bHash(const std::string str)
+{
+    // Daniel Bernstein hash fn 
+    u_int32_t h = 0;
+    for (std::string::const_iterator i = str.begin(); i < str.end(); i++)
+        h = 33*h + *i;
+    return h;
+}
+
 std::string MessageStoreImpl::getJrnlDir(const char* queueName) //for exmaple /var/rhm/ + queueDir/
 {
     std::stringstream dir;
     dir << getJrnlBaseDir() << std::hex << std::setfill('0') << std::setw(4);
-    u_int32_t count = 0;
-    for (u_int32_t i = 0; i < strlen(queueName); i++) {
-        count += queueName[i];
-    }
-    dir << (count % 29); // Use a prime number for better distribution across dirs
+    dir << (bHash(queueName) % 29); // Use a prime number for better distribution across dirs
     dir << "/" << queueName << "/";
     return dir.str();
 }

Modified: store/trunk/cpp/lib/MessageStoreImpl.h
===================================================================
--- store/trunk/cpp/lib/MessageStoreImpl.h	2009-01-07 20:10:31 UTC (rev 3034)
+++ store/trunk/cpp/lib/MessageStoreImpl.h	2009-01-08 14:53:33 UTC (rev 3035)
@@ -241,6 +241,7 @@
 
     // journal functions
     void createJrnlQueue(const qpid::broker::PersistableQueue& queue);
+    u_int32_t bHash(const std::string str);
     std::string getJrnlDir(const qpid::broker::PersistableQueue& queue); //for exmaple /var/rhm/ + queueDir/
     std::string getJrnlDir(const char* queueName);
     std::string getJrnlBaseDir();