Hi Richard, With the serialization optimizations you optimize only the second and third level stores, i.e. the runtime memory is still the almost same. You'll gain only if you have bigger second level cache which is used when the user uses browser back button. And I think this is no so often.
About Scala vs. Java consciousness: I guess you read this thread - http://groups.google.com/group/scala-user/browse_thread/thread/ea4d4dda2352a523# Here and in the previous thread on this topic the functional guys suggest solutions which I think are not that easy to read and as proven the speed is far from the imperative solution. Oderski explains it well in his response. About the questions - the simple answer is that a Component can have just one parent, so it is not possible to reuse it neither in the same page nor in different page. The same is true about its collection of children. This is the current state. On Wed, Jul 20, 2011 at 7:44 PM, Igor Vaynberg <igor.vaynb...@gmail.com> wrote: > On Wed, Jul 20, 2011 at 9:00 AM, richard emberson > <richard.ember...@gmail.com> wrote: >> I have many examples of such Java bloat. Consider the getKey method >> in the org/apache/wicket/util/value/ValueMap.java class: >> >> Java version: >> >> public String getKey(final String key) >> { >> for (Object keyValue : keySet()) >> { >> if (keyValue instanceof String) >> { >> String keyString = (String)keyValue; >> if (key.equalsIgnoreCase(keyString)) >> { >> return keyString; >> } >> } >> } >> return null; >> } >> >> Scala version: >> >> def getKey(key: String): Option[String] = >> keySet find { s => key.equalsIgnoreCase(s) } > > that is a bad example. that method was there since the times valuemaps > supported non-string keys, thats what all the noise was about. your > code doesnt support non string keys, and i just cleaned it up ours so > it doesnt have to worry about it either. thanks for pointing it out :) > > here it is in its concise form : > public String getKey(String key) { > for (String other : keySet()) if (other.equalsIgnoreCase(key)) return > other; > return null; > } > > it all depends on formatting >> >> The Scala version reads like a sentence: "For the keys find >> the key which equals, ignoring case, the key parameter." >> The Java code is just so sad in comparison. > > not in my concise version, though, is it? however, the concise version > is harder for some people to read, so we use very generous formatting > rules when it comes to spacing and curly braces. > >> I did have 2 questions buried in my previous email. >> Both having to do with serialization of an object when >> it appears as 2nd (3rd, etc.) time during the serialization >> process. > > serialization handles multiple references to the same instance. so if > you have the same instance showing up more then once in the > serialization graph it is only written out once. this is how circular > references are handled as well. > >> So, first, is it possible, likely, allowed, excluded, etc. that >> the same Component can appear more than once in the same >> Page tree? Would it make sense or even be possible for the >> same Form object to appear more than once in the same Page tree? >> Not two copies of a Form, but the single instance in two places >> on a Page? >> If it should never happen, is there code in Wicket that ensures >> that it does not happen? > > it is not allowed, see page#componentRendered() > >> Secondly, for a Component that is immutable in a given Page, >> could it appear, be reused, in the "same" Page in different >> Sessions (different clients)? Other areas of such Pages would >> be different, hold different data, but could the immutable part >> be same object? As an example, a read-only Label object, could >> it be used in the same place in the same Page "type" but in >> different Sessions? Is there any mechanism in Wicket currently >> that could identify such possible reuse? > > sharing component instances between pages is a bad idea, sharing them > between sessions is even worse. code is constantly refactored, what is > immutable now will most likely not be immutable later. i would hate > coding wicket if every time i made a change to someone else's > component i would have to check if i just made something immutable > mutable and possibly cause a security leak. > > -igor > > >> After memory comes performance and thats a much harder nut to >> crack. To track down bugs in the Scala port I had to put >> detailed logging into both the Java and Scala versions. >> What was most surprising was the amount a code that >> had to be execute, multiple times, just to render the >> simplest Page in a unit test - tens of pages of logging >> output. I do not understand all that is truly happening >> within Wicket to render a Page yet, but its on my todo list. >> And, maybe, there is no issue. >> >> Richard >> Thanks. >> >> >> On 07/20/2011 03:04 AM, Martin Grigorov wrote: >>> >>> Hi Richard, >>> >>> 1. Scala traits are something useful which I hope to have someday in Java >>> too. >>> They can help in make some code reusable when it is not possible to >>> have common base class. At the end a trait is a partial base class... >>> >>> 2. I'm not sure what problem you are after with this optimization in >>> the serialized version of the object (its bytes). >>> Your quest will not improve the runtime memory consumption because the >>> trait's properties are mixed with the class instance properties. You >>> may have problems with PermGen though because Scala produces classes >>> for every "with Foo" (and for every Function/closure). >>> You are trying to improve the size (and speed?) of the produced bytes >>> after serialization. While this will reduce the size of the page >>> caches (for two of them - second (application scope) and third >>> (disk)). First level (http session) contains page instances (not >>> serialized). Check https://cwiki.apache.org/confluence/x/qIaoAQ for >>> more information. >>> >>> RAM and especially HDD are cheap today, so I think the benefit of your >>> optimization will not be big. As a proof I can say that there are no >>> complains in the mailing lists that Wicket produces too big files for >>> the third level cache. The general complain is that http session >>> footprint is bigger than action-based web frameworks but I think this >>> is because using custom o.a.w.Session is so comfortable that people >>> start putting a lot of state there. The next reason is first-level >>> cache but even this is easy to "solve" - just implement custom >>> IPageManager or override the default one to not use http session as >>> first level cache. >>> >>> Recently we reworked a bit the code related to page serialization and >>> now it is possible to use any library specialized in object >>> serialization (see https://github.com/eishay/jvm-serializers/wiki). >>> The schema based ones (like Apache Avro, Thrift, Protobuf, ...) will >>> be harder to use but not impossible. >>> The schemaless ones (Java Serialization, Kryo, XStream, ...) are >>> easier to use with Wicket. You may check Kryo based serializer at >>> >>> https://github.com/wicketstuff/core/tree/master/jdk-1.6-parent/serializer-kryo >>> . It is faster than Java Serialization and produces less bytes. >>> >>> On Wed, Jul 20, 2011 at 2:43 AM, richard emberson >>> <richard.ember...@gmail.com> wrote: >>>> >>>> Martin, >>>> >>>> The reason I was interested in Wicket memory usage was because >>>> of the potential use of Scala traits, rather than the two possible >>>> Java approaches, might be compelling when it comes to memory usage. >>>> >>>> First, the two Java approaches: proxy/wrapper object or bundle everything >>>> into the base class. >>>> >>>> The proxy/wrapper approach lets one have a single implementation >>>> that can be share by multiple classes. The down side is that >>>> proxy/wrapper object requires an additional reference in the >>>> class using it and hence additional memory usage. >>>> >>>> The bundle everything into the base class approach violates >>>> OOP 101 dictum about having small objects focused on their >>>> own particular behavior thus avoiding bloat. >>>> (Not executable Java/Scala code below.) >>>> >>>> interface Parent { >>>> getParent >>>> setParent >>>> } >>>> // Potentially shared implementation >>>> class ParentProxy implements Parent { >>>> parent >>>> getParent = parent >>>> setParent(parent) = this.parent = parent >>>> } >>>> >>>> // Issue: Has additional instance variable: parentProxy >>>> class CompWithProxy with Parent { >>>> parentProxy = new ParentProxy >>>> getParent = parentProxy.getParent >>>> setParent(parent) = parentProxy.setParent(parent) >>>> } >>>> >>>> // Issue: Does not share implementation >>>> class CompAllInOne with Parent { >>>> parent >>>> getParent = parent >>>> setParent(parent) = this.parent = parent >>>> } >>>> >>>> Wicket has taken the "bundle everything into base class" in order >>>> to lessen memory usage - a certainly reasonable Java approach >>>> to the problem. >>>> >>>> With Scala one can do the following: >>>> >>>> // Shared implementation >>>> trait ParentTrait { >>>> parent >>>> getParent = parent >>>> setParent(parent) = this.parent = parent >>>> } >>>> >>>> // Uses implementation >>>> class Comp with ParentTrait >>>> >>>> The implementation, ParentTrait, can be used by any >>>> number of classes. >>>> In addition, one can add to a base class any number of >>>> such implementation traits sharing multiple implementations >>>> across multiple classes. >>>> >>>> So, can using such approach result in smaller (less in-memory) >>>> object in Scala than in Java? >>>> >>>> The ParentTrait does not really save very much. I assume >>>> that its only the Page class and sub-classes that do not have >>>> parent components in Wicket, so the savings per Page component >>>> tree is very small indeed. But, there are other behaviors that >>>> can be converted to traits, for example, Models. >>>> Many of the instance variables in the Java Models which >>>> take memory can be converted to methods return values which only >>>> add to the size of the class, not to every instance of the class. >>>> Also, with Model traits that use Component self-types, one can >>>> do away with IComponentAssignedModel wrapping and such. >>>> >>>> So, how to demonstrate such memory differences. I created >>>> stripped down versions of the Component and Label classes in >>>> both Java and Scala (only ids and Models) . >>>> Created different Model usage scenarios >>>> with Model object in Java and Traits in Scala, and, finally, >>>> serialized (Java Serialization) the result comparing the size >>>> of the resulting array of bytes. There are two runs, one with >>>> all Strings being the empty string and the next where all >>>> strings are 10-character strings: >>>> >>>> The Java versions (empty string): >>>> Label.Empty 99 >>>> Label.ReadOnly 196 >>>> Label.ReadWrite 159 >>>> Label.Resource 333 >>>> Label.Property 223 >>>> Label.ComponentProperty 351 >>>> Label.CompoundProperty 208 >>>> >>>> The Scala versions (empty string): >>>> Label.Empty 79 >>>> Label.ReadOnly 131 >>>> Label.ReadWrite 150 >>>> Label.Resource 164 >>>> Label.Property 207 >>>> Label.ComponentProperty 134 >>>> Label.CompoundProperty 184 >>>> >>>> >>>> The Java versions (10-character strings): >>>> Label.Empty 109 >>>> Label.ReadOnly 214 >>>> Label.ReadWrite 177 >>>> Label.Resource 359 >>>> Label.Property 241 >>>> Label.ComponentProperty 369 >>>> Label.CompoundProperty 218 >>>> >>>> >>>> The Scala versions (10-character strings): >>>> Label.Empty 89 >>>> Label.ReadOnly 149 >>>> Label.ReadWrite 168 >>>> Label.Resource 190 >>>> Label.Property 225 >>>> Label.ComponentProperty 152 >>>> Label.CompoundProperty 194 >>>> >>>> [Note that the Java Label.Empty result is misleading since in Wicket >>>> there is no memory overhead when a Component has no Model.] >>>> >>>> While this does indicate that using Model traits with Scala >>>> will result in less memory usage than the comparable Java >>>> approach, Java Serialization adds a whole lot of extra stuff >>>> to the array of bytes that masks the true change in >>>> in-memory usage. With Java Serialization, the class descriptor >>>> for each instance serialized is also added to the byte array and, >>>> it is this, that takes up most of the array of bytes. >>>> >>>> Thinking about it, I realized that Java Serialization is rather >>>> a blunt tool when it comes to the requirement of (Scala) Wicket >>>> Page serialization. Java Serialization creates a byte array >>>> that is rather self-contained/self-descriptive in its content. >>>> This is not required for (Scala) Wicket which has very >>>> specific requirements and use-cases. >>>> >>>> But first, before I describe what I did, here are the results. >>>> The byte array size data for the serializer I created just to >>>> show that one can do a lot better than Java Serialization: >>>> >>>> The Scala versions (empty string): >>>> Label.Empty 6 >>>> Label.ReadOnly 8 >>>> Label.ReadWrite 8 >>>> Label.Resource 10 >>>> Label.Property 13 >>>> Label.ComponentProperty 8 >>>> Label.CompoundProperty 11 >>>> >>>> The Scala versions (10-character strings): >>>> Label.Empty 8 >>>> Label.ReadOnly 12 >>>> Label.ReadWrite 12 >>>> Label.Resource 16 >>>> Label.Property 17 >>>> Label.ComponentProperty 12 >>>> Label.CompoundProperty 13 >>>> >>>> Yes, better by more than a factor of 10. I assume factors >>>> of 10 are compelling. >>>> >>>> So, back to the requirements. I spent a couple of days creating >>>> the serializer (currently 3.8Kloc) that focused on what I thought >>>> would be needed by (Scala) Wicket. >>>> The same application using (Scala) Wicket is running on either a >>>> single machine or a group of machines. >>>> The serialized Page system can have: >>>> >>>> In-memory repository >>>> (single-machine, testing); >>>> In-memory cache with local disk backstore >>>> (single-machine, production, re-start) and >>>> In-memory cache with database backstore used by a number of machines >>>> (multi-machine, production, fail-over, session-migration, re-start) >>>> >>>> Strings and associated id are cached/backstored where it is the id >>>> that is used in the serialized array. >>>> Classes and associated id are cached/backstored where it is the id >>>> that is used in the serialized array. >>>> Optimizations allow, for example, the Long value 1L to be serialized >>>> as 1 byte or (un-optimized) as 9 bytes. >>>> When using a backstore, a header is prepended to each byte array >>>> that includes the serializer magic number (2 bytes), serializer >>>> protocol version (2 bytes?) and application information (version, >>>> etc.) >>>> (2 bytes?). >>>> >>>> In addition, there are two cases where one might be serializing >>>> the same object more than once. >>>> >>>> The first case is dealt with by most serializers, an object >>>> appears more than once in the tree of objects being serialized. >>>> Java Serialization deals with this. One must keep track of >>>> the identity of all objects being serialized. Then, if an object >>>> appears for serialization for a second (third, etc.) time, some >>>> sort of reference object and tag is serialized rather than the >>>> object. De-serialization is .... obvious. >>>> I do not know, but I assume that this does not arise in Wicket; the >>>> same Component appearing more than once in the same Page tree of >>>> components. If it does happen, please let me know. If it should >>>> not happen but could, is there some visitor well-formness traversal >>>> that check for duplicate object appearances in a given tree? >>>> >>>> The second case is one that probably does (or could) occur with >>>> Wicket and I've never heard of a serializer dealing with, namely, >>>> the same object appears in more than one Page tree - knowledge >>>> of what is being serialized is shared across serializations. >>>> For this to work, the >>>> Component (which could be a tree of Components) has to be >>>> immutable like a Label with a read-only value or read-only Model >>>> (and the Model object is never changed), etc. Here, there can be >>>> a saving if the shared object is serialized in its own backstore >>>> and only its identifier appears in the byte arrays of each Page. >>>> If there was an Immutable interface which could tag immutable >>>> objects, it would be much easier for the serializer to identify >>>> them (well, not just easier, but, rather, plain old possible >>>> versus impossible) - just a last minute thought. >>>> >>>> I've not create a Java version of my serializer. But, since the >>>> Scala version does not use much Scala magic, a Java version >>>> would not be too hard to port to. I also have some 500 unit tests. >>>> >>>> Well, enough for now. >>>> >>>> Richard >>>> >>>> >>>> >>>> >>>> >>>> On 07/10/2011 02:37 AM, Martin Grigorov wrote: >>>>> >>>>> Hi, >>>>> >>>>> About the use cases: my experience is that most of the time the uses >>>>> the in-memory pages (for each listener callback execution, for ajax >>>>> requests,...). >>>>> Previous version of a page, or previous page is needed when the user >>>>> clicks browser back button. Even in this case most of the time the >>>>> in-memory cache is hit. Only when the user goes several pages back and >>>>> this page is not in-memory then the disk store is used. >>>>> >>>>> So far so good, but...! Even in-memory store contains serialized >>>>> versions of the Page, named SerializedPage. This is a struct which >>>>> contains >>>>> { >>>>> sessionId: String, >>>>> pageId: int, >>>>> data: byte[] >>>>> } >>>>> so the Page is serialized back and forth when stored in *any* >>>>> IPageStore/IDataStore. >>>>> >>>>> This is the current state in Wicket 1.5. >>>>> >>>>> Me and Pedro noticed that IPageStore impl (DefaultPageStore) can be >>>>> improved to work with Page instances but we decided to postpone this >>>>> optimization for 1.5.0+. >>>>> >>>>> About new String("someLiteral"): I don't remember lately seeing this >>>>> code neither in libraries, nor in applications. This constructor >>>>> should be used only when the developer explicitly wants this string to >>>>> not be interned and stored in the PermGen space, i.e. it will be >>>>> stored in the heap space. >>>>> Your benchmark test tests exactly this - the heap space. >>>>> I'll try the app with MemoryMXBean to see whether the non-heap changes >>>>> after deserialization. >>>>> I'm not very into Java Serialization but indeed it seems the Strings >>>>> are deserialized in the heap. But even in this case they go in the >>>>> Eden space, i.e. they are reclaimed soon after. >>>>> >>>>> On Sun, Jul 10, 2011 at 2:37 AM, richard emberson >>>>> <richard.ember...@gmail.com> wrote: >>>>>> >>>>>> I you run the little Java program I included, you will see that >>>>>> there is an impact - de-serialized objects take more memory. >>>>>> >>>>>> Richard >>>>>> >>>>>> On 07/09/2011 05:23 PM, Igor Vaynberg wrote: >>>>>>> >>>>>>> string literals are interned by the jvm so they should have a minimal >>>>>>> memory impact. >>>>>>> >>>>>>> -igor >>>>>>> >>>>>>> On Sat, Jul 9, 2011 at 5:10 PM, richard emberson >>>>>>> <richard.ember...@gmail.com> wrote: >>>>>>>> >>>>>>>> Martin, >>>>>>>> >>>>>>>> The reason I was interested was because it struck me a couple of >>>>>>>> days ago that while each Page, tree of Components, is created >>>>>>>> many (almost all?) of the non-end-user-generated Strings stored >>>>>>>> as instance variables in the tree are shared >>>>>>>> between all copies of the Page but that when such a Page is >>>>>>>> serialized to disk and then de-serialized, each String becomes its >>>>>>>> own >>>>>>>> copy unique to that particular Page. This means that if an >>>>>>>> appreciable number of Pages in-memory are reanimated Pages, then >>>>>>>> there could be a bunch of memory being used for all the String >>>>>>>> copies. >>>>>>>> >>>>>>>> In the attached simple Java file (yes, I still write Java when I >>>>>>>> must) >>>>>>>> there are three different ways of creating an array of >>>>>>>> Label objects (not Wicket Label) where each Label takes a String: >>>>>>>> new Label(some_string) >>>>>>>> >>>>>>>> The first is to share the same String over all instance of the Label. >>>>>>>> new Label(the_string) >>>>>>>> The second is to make a copy of the String when creating each >>>>>>>> Label; >>>>>>>> new Label(new String(the_string)) >>>>>>>> The third is to create a single Label, serialize it to an array of >>>>>>>> bytes and then generate the Labels in the array by de-serialized >>>>>>>> the byte array for each Label. >>>>>>>> >>>>>>>> Needless to say, the first uses the least memory; the label string >>>>>>>> is shared by all Labels while the second and third approach >>>>>>>> uses more memory. Also, if during the de-serialization process, the >>>>>>>> de-serialized String is replaced with the original instance of the >>>>>>>> String, then the third approach uses only as much memory as the >>>>>>>> first approach. >>>>>>>> >>>>>>>> No rocket science here, but it does seem to imply that if a >>>>>>>> significant number of Pages in-memory are actually reanimated Pages, >>>>>>>> then there could be a memory saving by >>>>>>>> making de-serialization smarter about possible shared objects. >>>>>>>> Even it it is only, say, a 5% saving for only certain Wicket >>>>>>>> usage patterns, it might be worth looking into. >>>>>>>> >>>>>>>> Hence, my question to the masters of Wicket and developers whose >>>>>>>> application might fit the use-case. >>>>>>>> >>>>>>>> Richard >>>>>>>> >>>>>>>> On 07/09/2011 11:03 AM, Martin Makundi wrote: >>>>>>>>> >>>>>>>>> Difficult to say ... we have disabled page versioning and se dump >>>>>>>>> sessions onto disk every 5 minutes to minimize memory hassles. >>>>>>>>> >>>>>>>>> But I am no master ;) >>>>>>>>> >>>>>>>>> ** >>>>>>>>> Martin >>>>>>>>> >>>>>>>>> 2011/7/9 richard emberson<richard.ember...@gmail.com>: >>>>>>>>>> >>>>>>>>>> This is a question for Wicket masters and those application >>>>>>>>>> builders >>>>>>>>>> whose application match the criteria as specified below. >>>>>>>>>> >>>>>>>>>> [In this case, a Wicket master is someone with a knowledge >>>>>>>>>> of how Wicket is being used in a wide spectrum of applications >>>>>>>>>> so that they have a feel for what use-cases exist in the real >>>>>>>>>> world.] >>>>>>>>>> >>>>>>>>>> Wicket is used in a wide range of applications with a variety of >>>>>>>>>> usage patterns. What I am interested in are those applications >>>>>>>>>> where >>>>>>>>>> an appreciable number of the pages in memory are pages that had >>>>>>>>>> previously been serialized and stored to disk and then reanimated, >>>>>>>>>> not found in an in-memory cache and had to be read from disk and >>>>>>>>>> de-serialized back into an in-memory page; which is to say, >>>>>>>>>> applications with an appreciable number of reanimated pages. >>>>>>>>>> >>>>>>>>>> Firstly, do such applications exists? These are real-world >>>>>>>>>> applications where a significant number of pages in-memory >>>>>>>>>> are reanimated pages. >>>>>>>>>> >>>>>>>>>> For such applications, what percentage of all pages at any >>>>>>>>>> given time are reanimated pages? >>>>>>>>>> Is it, say, a couple of percent? Two or three in which case its not >>>>>>>>>> very significant. >>>>>>>>>> Or, is it, say, 50%? Meaning that half of all pages currently in >>>>>>>>>> memory had been serialized to disk, flushed from any in-memory >>>>>>>>>> cache >>>>>>>>>> and then, as needed, de-serialized back into a Page. >>>>>>>>>> >>>>>>>>>> Thanks >>>>>>>>>> >>>>>>>>>> Richard >>>>>>>>>> -- >>>>>>>>>> Quis custodiet ipsos custodes >>>>>>>>>> >>>>>>>>>> >>>>>>>>>> --------------------------------------------------------------------- >>>>>>>>>> To unsubscribe, e-mail: users-unsubscr...@wicket.apache.org >>>>>>>>>> For additional commands, e-mail: users-h...@wicket.apache.org >>>>>>>>>> >>>>>>>>>> >>>>>>>>> >>>>>>>>> >>>>>>>>> --------------------------------------------------------------------- >>>>>>>>> To unsubscribe, e-mail: users-unsubscr...@wicket.apache.org >>>>>>>>> For additional commands, e-mail: users-h...@wicket.apache.org >>>>>>>>> >>>>>>>>> >>>>>>>> >>>>>>>> -- >>>>>>>> Quis custodiet ipsos custodes >>>>>>>> >>>>>>>> >>>>>>>> --------------------------------------------------------------------- >>>>>>>> To unsubscribe, e-mail: users-unsubscr...@wicket.apache.org >>>>>>>> For additional commands, e-mail: users-h...@wicket.apache.org >>>>>>>> >>>>>>> >>>>>>> --------------------------------------------------------------------- >>>>>>> To unsubscribe, e-mail: users-unsubscr...@wicket.apache.org >>>>>>> For additional commands, e-mail: users-h...@wicket.apache.org >>>>>>> >>>>>>> >>>>>> >>>>>> -- >>>>>> Quis custodiet ipsos custodes >>>>>> >>>>>> --------------------------------------------------------------------- >>>>>> To unsubscribe, e-mail: users-unsubscr...@wicket.apache.org >>>>>> For additional commands, e-mail: users-h...@wicket.apache.org >>>>>> >>>>>> >>>>> >>>>> >>>>> >>>> >>>> -- >>>> Quis custodiet ipsos custodes >>>> >>>> --------------------------------------------------------------------- >>>> To unsubscribe, e-mail: users-unsubscr...@wicket.apache.org >>>> For additional commands, e-mail: users-h...@wicket.apache.org >>>> >>>> >>> >>> >>> >> >> -- >> Quis custodiet ipsos custodes >> >> --------------------------------------------------------------------- >> To unsubscribe, e-mail: users-unsubscr...@wicket.apache.org >> For additional commands, e-mail: users-h...@wicket.apache.org >> >> > > --------------------------------------------------------------------- > To unsubscribe, e-mail: users-unsubscr...@wicket.apache.org > For additional commands, e-mail: users-h...@wicket.apache.org > > -- Martin Grigorov jWeekend Training, Consulting, Development http://jWeekend.com --------------------------------------------------------------------- To unsubscribe, e-mail: users-unsubscr...@wicket.apache.org For additional commands, e-mail: users-h...@wicket.apache.org
