Czekając w kolejce do bankomatu zauważyłem, że dwie osoby przede mną odchodzą nie pobierając gotówki. Gdyby to była tylko jedna osoba pomyślałbym, że chodzi o brak środków na koncie. Gdy druga osoba odebrała kartę obstawiałem problem z bankomatem. Postanowiłem sprawdzić co jest przyczyną problemów.

Na pierwszym ekranie widocznym po włożeniu karty pojawiło się pytanie:

Czy potrzebujesz gotówki?

Poniżej znajdowały się dwa przyciski: TAK i NIE. Pytanie wydało mi się dziwne jak na bankomat sieci Euronet.

Kiedy użytkownik wybierał “TAK” (przecież po gotówkę przyszedł do bankomatu) kierowany był na stronę ze szczegółami reklamy kredytów gotówkowych i “głupiał”. Użytkownik oczekiwał przecież pojawienia się menu bankomatu, dostawał coś mylącego. Rezygnował więc z transakcji (“bankomat zepsuty”) i odchodził.

Aby móc dokończyć transakcję należało wybrać “NIE” – dalej procedura przebiegała już standardowo.

Tak oto z mojego małego doświadczenia można wnioskować, że prosty błąd popełniony na etapie projektowania interfejsu użytkownika potrafi zniechęcić większość potencjalnych użytkowników systemu. Nie był to błąd działania systemu (nie poleciał żaden wyjątek, salda zachowały poprawną wartość), ale operacja do której bankomat był stworzony nie doszła do skutku.

Stało się tak, ponieważ przy integracji komponentów (nowa wersja reklamy w istniejącym UI bankomatu) nie sprawdzono jak całość zostanie odebrana przez klientów. Nie dokonano “testów integracyjnych na poziomie interfejsów białkowych”. Z moich doświadczeń wynika, że styk człowiek-komputer jest trudniejszy do oprogramowania niż interfejsy pomiędzy komponentami oprogramowania.

                          

If you created your repo copy by “clone” operation you will have “origin” remote branch defined. This remote can be used to pull/push changes.

$ git remote -v
origin zeus.aplikacja.info:cust-proj1

If you decide to change this definition later you can issue the following commands:

$ git remote rm origin
$ git remote add origin git@github.com:aplikacjainfo/proj1.git
$ sed -i '/\[branch "master"\]/a\\tremote = origin\n\tmerge = refs/heads/master' .git/config

The last step can be performed by any text editor.

After this change you can push your commits to new repository location (origin is selected as default remote branch for master, it’s configured in .git/config):

$ git push

That’s all. Much simpler than moving Subversion repository.

                          

Anyway, the most important difference to previous projects is “new” language: no more Java, no more Python, it’s C++. You can find few C++ projects I published on SourceForge, but they’re created >5 years old now, so I can use “new” word here . The first thought of old Test Driven Design fan when creating development environment was: whre’s JUnit for C++?

CppUnit

CppUnit is the most known port of Junit to C++ world. It’s pretty mature, full-featured (am I hearing “fat”?) and … verbose. See the code example:

// Simplest possible test with CppUnit
#include
class SimplestCase : public CPPUNIT_NS::TestFixture
{
    CPPUNIT_TEST_SUITE( SimplestCase );
    CPPUNIT_TEST( MyTest );
    CPPUNIT_TEST_SUITE_END();
protected:
    void MyTest();
};

CPPUNIT_TEST_SUITE_REGISTRATION( SimplestCase );  

void SimplestCase::MyTest()
{
    float fnum = 2.00001f;
    CPPUNIT_ASSERT_DOUBLES_EQUAL( fnum, 2.0f, 0.0005 );
}

It’s very verbose, indeed. Initially, I wanted to go in that direction but noticed much simpler syntax for declaring tests:

#include "lib/TestHarness.h"  

TEST (Whatever,MyTest)
{
    float fnum = 2.00001f;
    CHECK_DOUBLES_EQUAL (fnum, 2.0f);
}

What was the library?

CppUnitLite

CppUnitLite was written by Michael Feathers, the original author of CppUnit, who decided to leave CppUnit and write something smaller / lighter (do you know this feeling ). That’s why CppUnitLite was born.

CppUnit automatically discovers test cases based on TEST macro and organizes those tests into test suites. Small original code modications allows us to run:

• single test
• single test suite
• any combination of above

I see GoogleTest uses similar syntax for tests declarations. We will switch in the future if CppUnitLite features become too small for our requirements. At this very moment all needs are fulfilled:

• simple, easy to use syntax
• many assertions for comparing results
• light (important for embedded device)

Do you know of another C++ library that is worth considering?

                          

First, ensure all files group are switched to desired group:

find . ! -group group1 -exec chgrp group1 '{}' \;

Then +s (sticky) bit must be attached to directories to ensure group will be preserved in newly created directories:

find . -type d ! -perm -g=s -exec chmod g+s '{}' \;

Then writeability for the group should be set:

find . -type d ! -perm -g=w -exec chmod g+w '{}' \;

And finally some users must be added to the group:

adduser user1 group1

Additionally you have to set default umask to 0002 (only o+w filtered out). It’s done by installing libpam-umask and adding to /etc/pam.d/common-session:

session    optional     pam_umask.so umask=002

That’s all.

                          

SQL Error: 17006, SQLState: null Invalid column name

In order to track the problem down I enabled SQL logging and collected SQL query issued, then run it under SQL monitor and … it was working without error! I was surprised.

In order to debug what’s going on I enabled detailed logging in Hibernate. What was happened then?

[INFO] could not read column value from result set: entityKey215_0_; Invalid column name

This message showed me that the problem was not related to generated SQL query but to column names expected by Hibernate. Generated recordset didn’t has entityKey215_0_ column. I added:

entityKey AS {list.entityKey}

to named SQL query and error dissapeared.

This error is not-very-obvious kind of error because Oracle hides column / table names in error messages returned. Why? I don’t get this cryptic error messages idea. In order to track an error under Oracle I had to enable verbose logging (error message standalone din’t give anything useful). Much simpler database MySQL has better error reporting than “fat” Oracle.

                          

ConfigurationException: XML-22101: (Fatal Error) DOMSource node as this type not supported

This error may be caused by missing XML library bindings. In order to fix that error you have to configure properly some service providers (point JVM to correct XML parsing/transformation implementations).

How to do that? You have to create the following directory structure somewhere under classpath:

• META-INF
• META-INF/services
• META-INF/services/interface_name_files

Then inside “services” directory place filenames named after interfaces and filled with full class name of an implementation, for example (Xerces + Xalan plugged in):

• src/META-INF/services/javax.xml.parsers.DocumentBuilderFactory
  • org.apache.xerces.jaxp.DocumentBuilderFactoryImpl
• src/META-INF/services/javax.xml.parsers.SAXParserFactory
  • org.apache.xerces.jaxp.SAXParserFactoryImpl
• src/META-INF/services/javax.xml.transform.TransformerFactory
  • org.apache.xalan.processor.TransformerFactoryImpl

After this change proper XML implementation should be used (if the jar is present on classpatch of course).

                          

Fortunately current version of GIT supports that nice feature. It can be enabled with few settings in ~/.gitconfig file:

[diff]
color = true

[pager]
color = true

[status]
color = true

Additionally pager used (less in my case) should support ANSI colors (~/.bash_profile):

export LESS="-R"

And now diffs are rendered using colors that improve readability (anyone who doesn’t review changesets before commit? ). Now diffs look much better on a X terminal:

                          

svn merge -c -19203 https://REPO_URL

In example above you do reverse merge of 19203 revision (note “-” sign before revision number). After that merge:

• Inspect if workspace compiles without errors
• If it’s OK: commit local changeset
• Notify 19203 committer about the change

In order to fix broken commit original author should do the opposite:

svn merge -c 19203 https://REPO_URL

(note there’s no “-” before revision number). Then:

• Correct changeset and test if workspace is not broken
• If it’s OK: commit local changeset (it will be nice to show original revision number in a comment)

                          

504 Gateway Time-out
nginx/0.7.64

Oto wynik monitora realizowanego przez site-uptime.net:

Jak widać serwis boryka się z problemem wydajności podobnie jak kilka miesięcy temu Twitter. Czyżby znowu “popularność zaskoczyła drogowców” ?

Aktualizacja (2010-06-13). Sytuacja nie wygląda najlepiej. Od tygodnia ciągłe pady i uptime 82%:

                          

org.apache.commons.logging.Log=org.apache.commons.logging.impl.SimpleLog
priority=1

Then we can configure SimpleLog back-end just declared in simplelog.properties:

org.apache.commons.logging.simplelog.defaultlog=warn
org.apache.commons.logging.simplelog.log.com.mycompany.package=debug

You place those two files on classpath, redeploy application and … NOTHING HAPPENS. Those files aren’t visible!

Why is it happening? Here’s the explanation:

• Default WebSphere class-loader is defined as PARENT_FIRST, that means WebSphere classpath is being searched in first place
• WebSphere ships with commons-logging.properties that selects JDK 1.4 logging back-end

That’s why your commons logging configuration is not visible.

How to fix that: place files inside /opt/IBM/WID61/pf/wps/properties directory (it’s the first entry on the classpath). Then those files will become visible and log level customisation is possible then.

                          

Przelewy wychodzące zwykle związane są z kosztami stałymi które ciężko jest zoptymalizować (kredyt, czynsz, media). Kiedy trzeba kontrolować koszty warto więc spojrzeć na historię operacji na karcie. Możemy (czasami z zaskoczeniem) zobaczyć ile wydaliśmy np. w ciągu ostatniego miesiąca. Ustawiamy więc filtrowanie na 1 miesiąc:

i oglądamy wyniki:

Wyniki wyglądają sensownie, więc może teraz sprawdzić historię za ostatnie dwa miesiące?

W podsumowaniu operacji czeka nas niespodzianka:

Dane wyglądają nieco, hm, nierealistycznie. Analizując szczegółową listę operacji widać wyraźnie, że podsumowanie nie odzwierciedla sumy z listy. Obroty na rachunku są źle sumowane.

Kiedy ten błąd jest widoczny? Muszą być spełnione dwa warunki:

• lista operacji na koncie nie mieści się na jednej stronie wyników i aktywuje się stronicowanie wyników
• dla danego konta jest aktywny kredyt hipoteczny z mechanizmem bilansującym (tzw. mPlan)

W przypadku aktywowania się stronicowania podsumowanie gubi informację o wybranym rodzaju operacji.

Dobry proces testowania powinien uwzględnić przypadki szczególne (aktywny mPlan + stronicowana lista wyników). Z tego co widzę taką kombinację pominięto przy wprowadzaniu nowej wersji oprogramowania w mBanku. Problem zgłosiłem, zobaczymy ile czasu Bank potrzebuje na reakcję w przypadku takiego (dość prostego) błędu. Mam nadzieję, że procedury wpływające bezpośrednio na stan konta nie mają tego typu defektów

                          

Note: all uptime buttons and images below are generated in real-time, you can click on images / baners to see reports with details directly from site-uptime.net.

MySpace

MySpace uptime

Facebook

Facebook uptime

Twitter

Twitter uptime

As you can see the “winner” in this category is: Twitter!

Site-uptime.net

site-uptime.net is a service that continuously monitors websites and allows to configure email / SMS notifications on downtime. May be helpful for professionals who care about accessibility and uptime of their services.

                          

I checked the logs and saw that URL called by AdWords:

http://my-site.com/?gclid=342343445345....

Generated 403 (Forbidden) server response. That was caused by recent change in Lighttpd filtering rules. I was paying for AdWords traffic but customer hit 403 error page. Ops!

In order to easily spot such problems in future I created the following scanner to easily find all error server responses.

awk '$9>=400' /var/log/lighttpd/access.log | less

If you are boring of 404 errors you can filter them out as well (leaving only 403 / 500 errors for investigation):

awk '$9>=400 && $9 != 404' /var/log/lighttpd/access.log | less

I discovered that the following URLs were inaccessible:

• /robots.txt (exclusion rules for web crawlers)
• /favicon.ico (icon used by web browsers)

Next step could be automation of this check (cron job that will send an alert if errant responses count is higher than N). It’s left as exercise for the reader.

                          

Sometimes you have to use another caching library that has no direct support for Hibernate. Here the Hibernate API comes into play. I’ll show you how to plug Websphere’s DistributedMap into Hibernate.

First: you have to map get/put requests into desired API. org.hibernate.cache.Cache is an interface that must be subclassed for this task. This class instance is created by Hibernate for every entity that will be cached (distinguished by regionName).

public class WebsphereCacheImpl implements Cache {
    private DistributedMap map;
    private String regionName;
    public WebsphereCacheImpl(DistributedMap map, String regionName) {
        this.map = map;
        this.regionName = regionName;
    }
    public void clear() throws CacheException {
        map.clear();
    }
    public Object get(Object key) throws CacheException {
        return map.get(getMapKey(key));
    }
    public String getRegionName() {
        return regionName;
    }
    public void put(Object key, Object value) throws CacheException {
        map.put(getMapKey(key), value);
    }
    public Object read(Object key) throws CacheException {
        return map.get(getMapKey(key));
    }
    public void remove(Object key) throws CacheException {
        map.remove(getMapKey(key));
    }
    public void update(Object key, Object value) throws CacheException {
    map.put(getMapKey(key), value);
    }
    private String getMapKey(Object key) {
        return regionName + "." + key;
    }
    (...)
}

Then you have to prepare factory for such obejcts:

public class WebsphereCacheProviderImpl implements CacheProvider {

    private DistributedMap distributedMap;

    public WebsphereCacheProviderImpl() throws NamingException {
        InitialContext ic = new InitialContext();
        distributedMap = (DistributedMap) ic.lookup("services/cache/cache1");
    }
    public Cache buildCache(String regionName, Properties arg1) throws CacheException {
        return new WebsphereCacheImpl(distributedMap, regionName);
    }
    public boolean isMinimalPutsEnabledByDefault() {
        return false;
    }
    public long nextTimestamp() {
        return new Date().getTime();
    }
    public void start(Properties arg0) throws CacheException {
    }
    public void stop() {
    }
}

Then new factory class must be registered in Hibernate configuration:

<property name="hibernate.cache.use_second_level_cache">true</property>
<property name="hibernate.cache.use_query_cache">true</property>
<property name="cache.provider_class">com.company.project.cache.WebsphereCacheProviderImpl</property>

And voila!

                          

Donald Knuth wrote in his famous paper Structured Programming with go to Statements (PDF)

We should forget about small efficiencies, say about 97% of the time: pre-mature optimization is the root of all evil

Since compilation is premature optimization, it is therefore, the root of all evil. Simple!

Pretty “smart” reasoning but stupid, IMHO.

He mentioned: “Every time I build my code, my entire code base is type-checked (…) I only care about the method and class that I am currently working on” – yeah, local code change may introduce errors in unexpected parts of a system. I would even use FindBugs if it will improve code quality and slow down total build time. Why? Because I think it’s better to allow compiler/lint-tool to control correctness during development process to find most errors as early as possible.

Janmyr assumes the only application of static typing for release preparation (production mode) is better software optimisation. Compiled languages are more efficient than interpreted because many type checks was performed during compile time time and they can be removed from run-time.

I do believe dynamically-typed languages are faster for rapid development (I do love Python, BTW), but there’s a hidden cost here. In order to make your code maintainable you have to prepare sufficient level of unit test coverage (I’m using 80% as minumul level for projects in dynamic languages). That’s why i’m introducing some kind of static typing by:

• lint-like tools for python: pylint, pychecker
• project-specific static analysers

I do agree, however, that modern languages are loosing static type-safety by moving configuration outside Java code (XML files, properties, Json) and coding logic in external dynamic sub-languages (JSP). Java gets more type safety from 1.5+ language contructs but most frameworks go in opposite direction.

Isn’t Dynamic Typing the Root of All Evil then?

Duck Typing Ducks?

                          

Dharmesh Shah, Hubspot (and author of the popular On Startups blog) presents “Inbound Marketing” term, mostly how to attract customers to your product using SEO (Search Engine Optimisation) techniques.

He believes “Outbound Maketing” (traditional channels like TV, phones, …) that gives results in ~1% cases will be replaced by “Inbound Marketing” in future (allow the people to find your product). Dharmesh shows three main channels of “Inbound Marketing”:

• Google (and search engines)
• Blogs
• Social Networks (Like Facebook)

                          

I googled around and found “The evils of commons-logging.jar and its ilk” article. It highlight some problems related to commons-logging usage:

1. Different commons-logging versions in one project mirrors DLL-hell problem
2. Collection logs from all sources into one stream has no bigger value for a developer
3. Advanced configuration is logging back-end dependant (appenders for log4j for example), so unified layer is not valuable here
4. Configuration is not intuitive and hard

I agree with 1, 3 and 4. 2 is questionable: sometimes logs sorted in one timeline allows for better error analysis.

slf4j is proposed as an alternative. It’s more modular and (probably) simpler that commons-logging. All configuration is a matter of placing selected implementation (slf4j-jdk14-1.5.8.jar for instance) jar on classpath. And voila! – logging is done thru JDK 1.4 logging. Quite simple.

                          

javax.naming.NameNotFoundException: Name "comp/UserTransaction" not found in context "java:"

you want to see what entries are visible in JNDI. No problem, place this code somewhere near lookup problem code location:

InitialContext ic = new InitialContext();
NamingEnumeration it = ic.list("java:comp");
System.out.println("JNDI entries:");
while (it.hasMore()) {
    NameClassPair nc = it.next();
    System.out.println("JNDI entry: " + nc.getName());
}

You will see all JNDI names availailable on console then (you can use your logging library instead of course).

                          

I plugged in the objectgrid.jar into hibernate configuration:

<property name="cache.provider_class">
com.ibm.websphere.objectgrid.hibernate.cache.ObjectGridHibernateCacheProvider
</property>

then saw the following exception during Hibernate initialisation:

[4/29/10 10:08:34:462 CEST] 00000069 RegisteredSyn E WTRN0074E:
Exception caught from after_completion synchronization operation:
java.lang.NoSuchMethodError:
org/hibernate/cache/CacheException.<init>(Ljava/lang/Throwable; )V
at com.ibm.ws.objectgrid.hibernate.cache.ObjectGridHibernateCache.getSession(
ObjectGridHibernateCache.java:149)
at com.ibm.ws.objectgrid.hibernate.cache.ObjectGridHibernateCache.put(
ObjectGridHibernateCache.java:385)
at org.hibernate.cache.UpdateTimestampsCache.invalidate(
UpdateTimestampsCache.java:67)

WXS expects CacheException(java.lang.Throwable) constructor, Hibernate API supports this constructor since version 3.2. Version 3.1 currently used in project doesn’t support this constructor (only CacheException(java.lang.Exception) is present). This issue forced Hibernate upgrade in the project. Note that no Hibernate version requirements found on official “requirements” page (huh?).

Conclusions:

• BIG BLUE is not a guarantee for high quality documentation
• Closed source is harder to implement (any problems put you in waiting support queue)
• “Big” != Good (IMHO), would you pay for read-only cache implementation $14,400.00 per PVU and deploy giant objectgrid.jar (15M) for this very purpose? Yikes!

I’m going to talk with project sponsor about better ways to spend money (my salary increase, maybe ). Seriously: free EHCache / OSCache are more than sufficient for the task. They are small and Open Source.

“Do not hire Godzilla to pull Santa’s sleigh, reindeers are better for this purpose” – Bart Simpson.

                          

Another story is man-in-the-middle attack possibility or faking DNS servers response. You (as customer opening the webpage) should ensure that you are connecting to website you intended to (fake bank websites are big risk for your money, so it’s important). That’s why certification is closely bundled with connection encryption.

I’ll show you how obtain and install SSL certificate under Lighttpd web server to make your website more trustworthy for your customers.

Fitrst, create directory structure that will make organisation easier:

# mkdir -p /etc/lighttpd/ssl/domain.com
# cd /etc/lighttpd/ssl/domain.com

Create server key (you will be prompted for a password) and CSR (Certificate Signing Request) that will be used for certification creation in one step:

# openssl req -newkey rsa:1024 -keyout domain.com.key -out domain.com.csr

Remove attached password (I do not want to have to pass the password on server restart):

# openssl rsa -in domain.com.key -out domain.com.nopass.key

Then, pass generated domain.com.csr to your SSL certificate provider. You will have to prove you own the domain (an email will be sent to root@domain.com with special URL). After succesfull verification certificate is created. Place (paste) this certificate inside /etc/lighttpd/ssl/domain.com.crt file.

Then you have to create pem file (not sure why it’s organised that way):

# cat domain.com.nopass.key domain.com.crt > domain.com.pem

Then you have to tell Lighttpd to handle SSL traffic for given IP address and port:

$SERVER["socket"] == "IP-ADDRESS-HERE:443" {
    ssl.engine = "enable"
    ssl.pemfile = "/etc/lighttpd/ssl/domain.com/domain.com.pem"
    ssl.ca-file = "/etc/lighttpd/ssl/domain.com/domain.com.crt"
}

First note: for SSL traffic you have to specify IP address, not domain name. SSL handshake is done BEFORE headers are sent to server, so name based virtual hosts are not possible (certificates must be checked).

Second note: if you use the same domain for HTTP and HTTPS traffic don’t have to specify server.document-root and other domain-related parameters. They will be borrowed from:

$HTTP["host"] = "domain.com" {
(...)

(plain HTTP) section.

Now browser redirected to https://domain.com should show you your web-application without warnings.

Happy SSL-ing!

                          

• Usługi mogą mieć różny czas trwania (i taki czas będzie rezerwowany w kalendarzu specjalisty)
• Można przypisać usługi do różnych specjalistów

Uruchomienie mechanizmu jest bardzo proste: po pierwsze definiujemy usługi i przypisujemy je do wybranych lekarzy (zakładka “Usługi”).

Od tego momentu pacjent w pierwszej kolejności wskazuje usługę którą jest zainteresowany:

Następnie wybiera specjalistę realizującego szukaną usługę (widzi opis i najbliższy dostępny termin):

Dalej procedura rejestracji postępuje jak dotychczas (z SMS-owym hasłem).

                          

Migrating SQL dump to different database dialect is not very easy (column types / dates formats as first examples come to mind). But you don’t have to operate on SQL dumps. The simple answer here is: “dumpdata”.

Django uses special manage.py script to manage typical operations like: initialisation of database, preloading data, dropping database etc. The command:

manage.py dumpdata appname

prints on stdout all data contained in appname in universal Json format. Then you can load dump just created by using:

manage.py sqlreset gabinet | psql ...
manage.py loaddata filename.json

Database state must be reset before import. That’s why sqlreset is used. sqlreset alone prints DROP DATABASE statements on stdout allows to purge database from tables (if passed to SQL execution tool).

Additionally you can gzip JSON data created to make migration (much) faster:

manage.py dumpdata appname | gzip -c | ssh destinationserv 'cat > data.json.gz'
(login to destinationserv ...)
manage.py sqlreset appname | psql ...
gzip -dc data.json.gz | manage.py loaddata -

Happy migrating!

                          

The property I’m going to present today is “mime-type“. It describes file content in similar way to HTTP header “Content-type” telling svn client how to handle the file. Typical values are: “text/plain”, “application/octet-stream”. Especially first part of mime-type is important:

• text/*: line-by-line merges are used, diffs are generated
• any other prefix: no text merges prepared

If you do not set this properly right you may end up with messed binary file (end-of-line conversions) or non-mergable changes in text file (that is marked as binary by mistake).

Of course during adding a file to workspace one can forget to set those properties correctly. Here auto-props comes with help. Auto-props are applied when “svn add” command (from command line or from GUI) is issued. Configuration is placed inside “~/.subversion/config” file. Here’s my config fragment from one of projects.

[auto-props]
*.csv = svn:mime-type=text/plain
*.java = svn:mime-type=text/plain
*.sql = svn:mime-type=text/plain
*.sql = svn:keywords=Author Date Id Revision URL
*.jar = svn:mime-type=application/octet-stream

Besides mime-type svn:keywords is being set in the example. It controls which keywords are expanded in source files.

                          

It’s very easy to install the tool under Debian-based systems:

apt-get install xclip

Collect huge selection into a file (if pasting into terminal may be very slow):

xclip -o > file_name.txt

Download selected URL into /tmp/file.out:

URL=`xclip -o`; test -z "$URL" || wget -O /tmp/file.out "$URL"

Place file contents into clipboard:

xclip -i < file_path

As you can see xclip is a handy tool built with unix-style elegance in mind. Many other applications could be discovered for this tool.

                          

rm -rf $WID_HOME/pf/wps/databases/BPEDB
echo "CONNECT 'jdbc:derby:$WID_HOME/pf/wps/databases/BPEDB;create=true' AS BPEDB;"|\
    $WID_HOME/runtimes/bi_v61/derby/bin/embedded/ij.sh /dev/stdin

                          

ID-based entity lookup cache

Caching entity-based lookup by id is very straightforward:

<session-factory>
    <property name="cache.provider_class">
        com.opensymphony.oscache.hibernate.OSCacheProvider
    </property>
    (...)
</session-factory>

<class name="EntityClass" table="ENTITY_TABLE">
   <cache usage="read-only" />
   (...)
</class>

Since then selecting EntityClass by id will use cache (BTW. remember to set cache expiration policy if entity is mutable!). But querying but other entity attributes will not cache the results.

Query cache

Here so-called “query cache” jumps in:

<session-factory>
    <property name="cache.use_query_cache">true</property>
    (...)
</session-factory>

Query query = new Query(EntityClass.class);
(...)
query.setCacheable(true);
query.list();

and voila! Queries issued (with parameters) are indices for cached results. The very important note is the value stored in cache. Entity keys and types are stored. Why is it important? Because it complicates caching SQL queries.

Caching SQL queries

Query cache requires query result to be Hibernate-known entity because the reason I mentioned above. That disallow to cache the following construct:

<!-- Map the resultset on a map. -->
<class name="com.comapny.MapDTO" entity-name="EntityMap">
<id name="entityKey" type="java.math.BigDecimal" column="ID" length="38"
access="com.company.MapPropertyAccessor" />
<property name="achLimit" type="java.lang.String" length="256" access="com.company.MapPropertyAccessor" />
</class>

<!-- alias is used in query -->
<resultset name="EntityMapList">
<return alias="list" entity-name="EntityMap" />
</resultset>

<sql-query name="NamedQueryName" resultset-ref="EntityMapList">
SELECT (...) AS {list.entityKey}
(...)
FROM TABLE_NAME
WHERE
(...)
</sql-query>

We will get the error:

Error: could not load an entity: EntityMap#1028
ORA-00942: table or view does not exist

EntityMap cannot be loaded separately by Hibernate because it’s a DTO (data transfer object), not the entity. How to fix this error? Just change result of named query from DTO to corresponding entity. Then entity retrieved will be cached properly by Hibernate.

                          

Random network instability visible during last days forced me to make a fast migration S1 to new server. Linode slice deployed in UK was choosen as default platform for S1 monitoring station. Their networks and servers proved to be very stable in past few years.

I hope new infrastructure will make better measurements and lower false notifications ratio.

                          

Jeden z moich klientów potrzebował udostępnić swoim pacjentom rezerwacje zmiennej długości (zależnej od rodzaju usługi). Zastosował on tymczasowe (przyznaję, sprytne) rozwiązanie polegające na rezerwacji dwóch kolejnych terminów dla dłuższej wizyty. Było ono jednak dość niewygodne dla pacjenta.

Dziś system został rozszerzony o możliwość definiowania usług (wraz z czasem), dzięki czemu wybór specjalisty i usługi jest wygodny. Zapraszam do zapoznania się z aktualną wersją systemu.