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Posted to dev@commons.apache.org by Juozas Baliuka <ba...@mwm.lt> on 2002/01/31 18:23:02 UTC
RE: Serious problem with MRUMap -- JCS LRU and MRUMap -- RE:
[simplestore] enhancements (was: [simplestore] inital check
in)
<skip>
>You should try to build it as a memory plugin for JCS. It might require
>some element attribute additions (what type of reference) if they are
>useful.
>
>The cache hub manages expiration at request time, this could be moved to
>a background thread. Cleanup of unused items could result in spooling.
Sorry, I can't use any "background cleanup" it has no meaning for memory cache.
This thread can remove objects from cache, but not from memory, if
application has strong reference on object.
"expiration at request time" has no meaning if application has strong
reference on object.
example situation :
...............................................
User u = cache.get(id);
if( u == null ){
u = User.create( id );
cache.put(id,u);
session.setAttribute("user",u);// I have strong reference here
team.add(u);
}
..............................................
request.setAttribute("player",u);
...............................................
Requests, operations , but I don't remove "user" from session
..............................................
assertTrue("try to increase sessin time out", session.isValid() );
// my session is valid at this time.
// cache must not remove my "user" if GC not decided to do this.
assertEquals("cache doe's not work or bug in GC ",
session.getAttribute("user"), cache.get(id));
Cache must release unused references, if memory is "low" and must never
remove object from cache if it used by application.
if this test fails I don't need this kind of cache, it can be very fast,
but not useful.
>JCS has a memory index of disk items. The performance is better than a
>B tree, but it takes some memory (around 1.5 Mb for 500,000 items, not
>much if you ask me.) There are also B tree disk plugins. . . . .
>
>
> >
> > I believe everything can be optimized, and thank you for help.
> >
> > At 12:23 AM 1/31/2002 -0500, you wrote:
> >
> > >I found this example of a MRUCache on the sun site and tried making a
> > >memory cache plugin with the technique.
> > >
> >
> >http://developer.java.sun.com/developer/onlineTraining/Programming/JDCB
>o
> > >ok/perf4.html
> > >
> > >The performance of the LinkedList remove function makes it unusable.
> > >They should deprecate it.
> > >
> > >I'm going to check the code into JCS as an example. I got around the
> > >remove problem for initial puts, since you can avoid a remove, but
>any
> > >updates will kill you. Since every get in this system requires an
> > >update of the linked list, it makes the technique unscalable.
> > >
> > >The simplestore MRUMap class is pretty much the same as this example,
> > >except it takes the remove hit for just about every operation, even
>an
> > >initial put.
> > >
> > >I've included some results and the main method I used to test the
>MRUMap
> > >below. Just watch the performance degrade.
> > >
> > >
> > >G:\dev\bin\classes>java MRUMap 1000 2
> > >took 111 ms. to put 1000
> > >took 170 ms. to get 1000
> > >took 160 ms. to put 1000
> > >took 150 ms. to get 1000
> > >
> > >G:\dev\bin\classes>java MRUMap 2000 2
> > >took 290 ms. to put 2000
> > >took 891 ms. to get 2000
> > >took 691 ms. to put 2000
> > >took 711 ms. to get 2000
> > >
> > >G:\dev\bin\classes>java MRUMap 3000 2
> > >took 1272 ms. to put 3000
> > >took 3365 ms. to get 3000
> > >took 3165 ms. to put 3000
> > >took 3645 ms. to get 3000
> > >
> > >G:\dev\bin\classes>java MRUMap 5000 2
> > >took 6389 ms. to put 5000
> > >took 16665 ms. to get 5000
> > >took 16764 ms. to put 5000
> > >took 16885 ms. to get 5000
> > >
> > >G:\dev\bin\classes>java MRUMap 9000 2
> > >took 26779 ms. to put 9000
> > >took 56403 ms. to get 9000
> > >took 51044 ms. to put 9000
> > >took 54429 ms. to get 9000
> > >
> > >
> > >(Oh, I depackaged the MRUMap to make it easier to work with. I
>attached
> > >it.)
> > >
> > >The test method for MRUMap:
> > >
> >
> >///////////////////////////////////////////////////////////////////////
>/
> > >//
> > >
> > > public static void main( String[] args ) {
> > >
> > > int size = 1000;
> > > if ( args.length > 0 ) {
> > > try {
> > > size = Integer.parseInt(args[0]);
> > > } catch ( NumberFormatException e ) {
> > > System.out.println( "arg 1 (size) should be a
>number" );
> > > }
> > > }
> > >
> > > int cycles = 2;
> > > if ( args.length > 1 ) {
> > > try {
> > > cycles = Integer.parseInt(args[1]);
> > > } catch ( NumberFormatException e ) {
> > > System.out.println( "arg 2 (cycles) should be a
>number"
> > >);
> > > }
> > > }
> > >
> > > MRUMap map = new MRUMap( size );
> > >
> > > boolean show = false;
> > > if ( args.length > 2 ) {
> > > try {
> > > show = Boolean.valueOf(args[2]).booleanValue();;
> > > } catch ( Exception e ) {
> > > System.out.println( "arg 3 (show) should be true or
> > >false" );
> > > }
> > > }
> > >
> > > for ( int i = 0; i < cycles; i++ ) {
> > > long startP = System.currentTimeMillis();
> > > for ( int j = 0; j <= size; j++ ) {
> > > map.put( "key" + j, "value" + j );
> > > }
> > > long endP = System.currentTimeMillis();
> > > long deltaP = endP - startP;
> > > System.out.println( "took " + deltaP + " ms. to put " +
>size
> > >);
> > >
> > > long startG = System.currentTimeMillis();
> > > for ( int j = 0; j <= size; j++ ) {
> > > String val = (String)map.get( "key" + j );
> > > if ( show ) {
> > > System.out.println( val );
> > > }
> > > }
> > > long endG = System.currentTimeMillis();
> > > long deltaG = endG - startG;
> > > System.out.println( "took " + deltaG + " ms. to get " +
>size
> > >);
> > >
> > > }
> > >
> > > } // end main
> > >
> >
> >\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\
>\
> > >\\\
> > >
> > >
> > >
> > >
> > >The bad method in java.util.LinkedList
> > >
> > >
> > >/////////////////////////////////////////////////////
> > > /**
> > > * Removes the first occurrence of the specified element in this
> > >list. If
> > > * the list does not contain the element, it is unchanged. More
> > >formally,
> > > * removes the element with the lowest index <tt>i</tt> such
>that
> > > * <tt>(o==null ? get(i)==null : o.equals(get(i)))</tt> (if such
>an
> > > * element exists).
> > > *
> > > * @param o element to be removed from this list, if present.
> > > * @return <tt>true</tt> if the list contained the specified
> > >element.
> > > */
> > > public boolean remove(Object o) {
> > > if (o==null) {
> > > for (Entry e = header.next; e != header; e = e.next) {
> > > if (e.element==null) {
> > > remove(e);
> > > return true;
> > > }
> > > }
> > > } else {
> > > for (Entry e = header.next; e != header; e = e.next) {
> > > if (o.equals(e.element)) {
> > > remove(e);
> > > return true;
> > > }
> > > }
> > > }
> > > return false;
> > > }
> > >
> > >/////////////////////////////////////////
> > >
> > >
> > >The LRUMemoryCache in JCS gets inside the linked list and doesn't
>suffer
> > >from these problems. On average, with 9000 items the cache JCS is
>over
> > >1000 time faster than the MRUMap.
> > >
> > >Here are some times from the JCS tester using only the memory cache.
> > >These tests went through the cache hub with all the added operations.
> > >
> > >putm 9000
> > >---put 9000 in 220 millis ---
> > >enter command:
> > >putm 9000
> > >---put 9000 in 180 millis ---
> > >enter command:
> > >putm 9000
> > >---put 9000 in 220 millis ---
> > >enter command:
> > >putm 9000
> > >---put 9000 in 221 millis ---
> > >enter command:
> > >getm 9000 false
> > >---got 9000 in 40 millis ---
> > >enter command:
> > >getm 9000 false
> > >---got 9000 in 60 millis ---
> > >enter command:
> > >getm 9000 false
> > >---got 9000 in 50 millis ---
> > >enter command:
> > >getm 9000 false
> > >---got 9000 in 50 millis ---
> > >
> > >
> > >[The configuration
> > >################## JCS CACHE REGIONS AVAILABLE ###################
> > ># Regions preconfirgured for caching
> > >jcs.region.testCache1=DC
> >
> >jcs.region.testCache1.cacheattributes=org.apache.stratum.jcs.engine.Com
>p
> > >ositeCacheAttributes
> > >jcs.region.testCache1.cacheattributes.MaxObjects=20000
> >
> >jcs.region.testCache1.cacheattributes.MemoryCacheName=org.apache.stratu
>m
> > >.jcs.engine.memory.lru.LRUMemoryCache
> > >]
> > >
> > >enter command:
> > >putm 20000
> > >---put 20000 in 761 millis ---
> > >enter command:
> > >getm 20000 false
> > >---got 20000 in 301 millis ---
> > >enter command:
> > >putm 20000
> > >---put 20000 in 781 millis ---
> > >enter command:
> > >getm 20000 false
> > >---got 20000 in 220 millis ---
> > >enter command:
> > >
> > >
> > >Another configuration (max mem at 1000, all gets shuffling, no
>getting
> > >of first element, hence all the gets at 2000 are from disk and memory
> > >elements are being replaced)
> > >
> > >[configuration
> > ># Regions preconfirgured for caching
> > >jcs.region.testCache1=DC
> >
> >jcs.region.testCache1.cacheattributes=org.apache.stratum.jcs.engine.Com
>p
> > >ositeCacheAttributes
> > >jcs.region.testCache1.cacheattributes.MaxObjects=1000
> >
> >jcs.region.testCache1.cacheattributes.MemoryCacheName=org.apache.stratu
>m
> > >.jcs.engine.memory.lru.LRUMemoryCache
> > >]
> > >
> > >enter command:
> > >putm 2000
> > >---put 2000 in 621 millis ---
> > >enter command:
> > >getm 2000 false
> > >---got 2000 in 1653 millis ---
> > >enter command:
> > >getm 2000 false
> > >---got 2000 in 1102 millis ---
> > >enter command:
> > >getm 2000 false
> > >---got 2000 in 1172 millis ---
> > >enter command:
> > >getm 2000 false
> > >---got 2000 in 1241 millis ---
> > >enter command:
> > >getm 2000 false
> > >---got 2000 in 1132 millis ---
> > >enter command:
> > >putm 2000
> > >---put 2000 in 170 millis ---
> > >enter command:
> > >putm 2000
> > >---put 2000 in 151 millis ---
> > >enter command:
> > >putm 2000
> > >---put 2000 in 100 millis ---
> > >enter command:
> > >putm 2000
> > >---put 2000 in 40 millis ---
> > >enter command:
> > >getm 2000 false
> > >---got 2000 in 1202 millis ---
> > >enter command:
> > >getm 2000 false
> > >---got 2000 in 1141 millis ---
> > >enter command:
> > >getm 2000 false
> > >---got 2000 in 1242 millis ---
> > >enter command:
> > >
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