22. public class BuzzwordDetector {
static String[] prefixes = { "synergy", "win-win" };
static String[] myArgs = { "clown synergy", "gorilla win-wins", "whamee" };
public static void main(String[] args) {
args = myArgs;
int buzzwords = 0;
for (int i = 0; i < args.length; i++) {
String lc = args[i].toLowerCase();
for (int j = 0; j < prefixes.length; j++) {
if (lc.contains(prefixes[j])) {
buzzwords++;
}
}
}
System.out.println("Found " + buzzwords + " buzzwords");
}
}
Wednesday, July 31, 13
23. New():
ref <- allocate()
if ref = null /* Heap is full */
collect()
ref <- allocate()
if ref = null /* Heap is still full */
error "Out of memory"
return ref
atomic collect():
markFromRoots()
sweep(HeapStart, HeapEnd)
From Garbage Collection Handbook
Wednesday, July 31, 13
24. markFromRoots():
initialise(worklist)
for each fld in Roots
ref <- *fld
if ref != null && not isMarked(ref)
setMarked(ref)
add(worklist, ref)
mark()
initialise(worklist):
worklist <- empty
mark():
while not isEmpty(worklist)
ref <- remove(worklist) /* ref is marked */
for each fld in Pointers(ref)
child <- *fld
if (child != null && not isMarked(child)
setMarked(child)
add(worklist, child)
From Garbage Collection Handbook
Wednesday, July 31, 13
40. ...
import java.lang.management.*;
...
public static long getCollectionTime() {
long collectionTime = 0;
for (GarbageCollectorMXBean mbean : ManagementFactory.getGarbageCollectorMXBeans())
{
collectionTime += mbean.getCollectionTime();
}
return collectionTime;
}
Available via JMX
Wednesday, July 31, 13
56. How can a client ignore GC-ing hosts?
Wednesday, July 31, 13
57. Server lies to clients about availability
TCP socket receive buffer
TCP write buffer
Wednesday, July 31, 13
58. “Banner” protocol
1. Connect via TCP
2.Wait ~1-10ms
3. Either receive magic four byte header or try another host
4. Only send query after receiving header from server
Wednesday, July 31, 13
76. #!/usr/bin/env bash
# This script is designed to be run every minute by cron.
host=$(hostname -s)
psout=$(ps h -p `cat /var/run/etsy-search.pid` -o min_flt,maj_flt 2>/dev/null)
min_flt=$(echo $psout | awk '{print $1}') # minor page faults
maj_flt=$(echo $psout | awk '{print $2}') # major page faults
epoch_s=$(date +%s)
echo -e "search_memstats.$host.etsy-search.min_fltt${min_flt:-0}t$epoch_s" | nc
graphite.etsycorp.com 2003
echo -e "search_memstats.$host.etsy-search.maj_fltt${maj_flt:-0}t$epoch_s" | nc
graphite.etsycorp.com 2003
Wednesday, July 31, 13
77. Solution 1: Buy more RAM
Ideally enough RAM to:
Keep data in OS file buffers
AND ensure no paging ofVM memory
AND whatever else happens on the box
~$5-10/GB
Wednesday, July 31, 13
78. echo “0” > /proc/sys/vm/swappiness
Wednesday, July 31, 13
