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Logging JVM and OS metrics in a spring application

Posted on February 23, 2015 by justme

We have a problem. We have an important application which is running in production, but we do not have access to details about the production system. When we get get reports of slowness, there is no way for us to see what was happening on the server at that time. Was memory low, CPU high, is it a garbage collection problem?

We basically wanted to get some insights added in our logs. Fortunately using metrics and metrics-spring this is easy using a configuration file like the following:

<beans xmlns="http://www.springframework.org/schema/beans"
       xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
       xmlns:metrics="http://www.ryantenney.com/schema/metrics"
       xsi:schemaLocation="
           http://www.springframework.org/schema/beans
           http://www.springframework.org/schema/beans/spring-beans-3.2.xsd
           http://www.ryantenney.com/schema/metrics
           http://www.ryantenney.com/schema/metrics/metrics-3.0.xsd">
 
    <!-- Registry should be defined in only one context XML file -->
    <metrics:metric-registry id="metrics" />
 
    <!-- (Optional) Registry should be defined in only one context XML file -->
    <metrics:reporter type="slf4j" metric-registry="metrics" period="1m" />
 
    <!-- The registry defines the data to capture. Metrics in this example require the metrics-jvm jar. -->
    <metrics:register metric-registry="metrics">
        <bean metrics:name="jvm.gc" class="com.codahale.metrics.jvm.GarbageCollectorMetricSet" />
        <bean metrics:name="jvm.memory" class="com.codahale.metrics.jvm.MemoryUsageGaugeSet" />
        <bean metrics:name="jvm.thread-states" class="com.codahale.metrics.jvm.ThreadStatesGaugeSet" />
        <bean metrics:name="os" class="be.vlaanderen.awv.dc.util.metrics.OperatingSystemGaugeSet" />
    </metrics:register>
 
</beans>

metrics-spring by default contains gauges to register the garbage collector behaviour, the memory usage and thread states (including info deadlocks). Is also contains a gauge for the number of file descriptors, but wanted to track more information including

committed virtual memory size
total swap space (size)
free swap space (size)
process CPU time
total physical memory (size)
free physical memory (size)
max file descriptor count
free file descriptor count
system CPU load (average for last minute)
process CPU load (average for last minute)

This can be done using the following class:

import com.codahale.metrics.Gauge;
import com.codahale.metrics.Metric;
import com.codahale.metrics.MetricSet;
 
import java.lang.management.ManagementFactory;
import java.lang.management.OperatingSystemMXBean;
import java.lang.reflect.InvocationTargetException;
import java.lang.reflect.Method;
import java.util.HashMap;
import java.util.Map;
import java.util.Optional;
 
/**
 * A set of gauges for operating system settings.
 */
public class OperatingSystemGaugeSet implements MetricSet {
 
    private final OperatingSystemMXBean mxBean;
    private final Optional<Method> committedVirtualMemorySize;
    private final Optional<Method> totalSwapSpaceSize;
    private final Optional<Method> freeSwapSpaceSize;
    private final Optional<Method> processCpuTime;
    private final Optional<Method> freePhysicalMemorySize;
    private final Optional<Method> totalPhysicalMemorySize;
    private final Optional<Method> openFileDescriptorCount;
    private final Optional<Method> maxFileDescriptorCount;
    private final Optional<Method> systemCpuLoad;
    private final Optional<Method> processCpuLoad;
 
    /**
     * Creates new gauges using the platform OS bean.
     */
    public OperatingSystemGaugeSet() {
        this(ManagementFactory.getOperatingSystemMXBean());
    }
 
    /**
     * Creates a new gauges using the given OS bean.
     *
     * @param mxBean an {@link OperatingSystemMXBean}
     */
    public OperatingSystemGaugeSet(OperatingSystemMXBean mxBean) {
        this.mxBean = mxBean;
 
        committedVirtualMemorySize = getMethod("getCommittedVirtualMemorySize");
        totalSwapSpaceSize = getMethod("getTotalSwapSpaceSize");
        freeSwapSpaceSize = getMethod("getFreeSwapSpaceSize");
        processCpuTime = getMethod("getProcessCpuTime");
        freePhysicalMemorySize = getMethod("getFreePhysicalMemorySize");
        totalPhysicalMemorySize = getMethod("getTotalPhysicalMemorySize");
        openFileDescriptorCount = getMethod("getOpenFileDescriptorCount");
        maxFileDescriptorCount = getMethod("getMaxFileDescriptorCount");
        systemCpuLoad = getMethod("getSystemCpuLoad");
        processCpuLoad = getMethod("getProcessCpuLoad");
    }
 
 
    @Override
    public Map<String, Metric> getMetrics() {
        final Map<String, Metric> gauges = new HashMap<>();
 
        gauges.put("committedVirtualMemorySize", (Gauge<Long>) () -> invokeLong(committedVirtualMemorySize));
        gauges.put("totalSwapSpaceSize", (Gauge<Long>) () -> invokeLong(totalSwapSpaceSize));
        gauges.put("freeSwapSpaceSize", (Gauge<Long>) () -> invokeLong(freeSwapSpaceSize));
        gauges.put("processCpuTime", (Gauge<Long>) () -> invokeLong(processCpuTime));
        gauges.put("freePhysicalMemorySize", (Gauge<Long>) () -> invokeLong(freePhysicalMemorySize));
        gauges.put("totalPhysicalMemorySize", (Gauge<Long>) () -> invokeLong(totalPhysicalMemorySize));
        gauges.put("fd.usage", (Gauge<Double>) () -> invokeRatio(openFileDescriptorCount, maxFileDescriptorCount));
        gauges.put("systemCpuLoad", (Gauge<Double>) () -> invokeDouble(systemCpuLoad));
        gauges.put("processCpuLoad", (Gauge<Double>) () -> invokeDouble(processCpuLoad));
 
        return gauges;
    }
 
    private Optional<Method> getMethod(String name) {
        try {
            final Method method = mxBean.getClass().getDeclaredMethod(name);
            method.setAccessible(true);
            return Optional.of(method);
        } catch (NoSuchMethodException e) {
            return Optional.empty();
        }
    }
 
    private long invokeLong(Optional<Method> method) {
        if (method.isPresent()) {
            try {
                return (long) method.get().invoke(mxBean);
            } catch (IllegalAccessException | InvocationTargetException ite) {
                return 0L;
            }
        }
        return 0L;
    }
 
    private double invokeDouble(Optional<Method> method) {
        if (method.isPresent()) {
            try {
                return (double) method.get().invoke(mxBean);
            } catch (IllegalAccessException | InvocationTargetException ite) {
                return 0.0;
            }
        }
        return 0.0;
    }
 
    private double invokeRatio(Optional<Method> numeratorMethod, Optional<Method> denominatorMethod) {
        if (numeratorMethod.isPresent() && denominatorMethod.isPresent()) {
            try {
                long numerator = (long) numeratorMethod.get().invoke(mxBean);
                long denominator = (long) denominatorMethod.get().invoke(mxBean);
                if (0 ==  denominator) {
                    return Double.NaN;
                }
                return 1.0 * numerator / denominator;
            } catch (IllegalAccessException | InvocationTargetException ite) {
                return Double.NaN;
            }
        }
        return Double.NaN;
    }
 
}

Done.

With this configuration, we get some info in the logs every minute, looking something like this:

~dc-local 2015-02-19T21:48:08.496+0100 [0.0.0.0-metrics-logger-reporter-thread-1] INFO  metrics - type=GAUGE, name=jvm.fd.usage, value=0.12158203125
~dc-local 2015-02-19T21:48:08.496+0100 [0.0.0.0-metrics-logger-reporter-thread-1] INFO  metrics - type=GAUGE, name=jvm.gc.PS-MarkSweep.count, value=6
~dc-local 2015-02-19T21:48:08.496+0100 [0.0.0.0-metrics-logger-reporter-thread-1] INFO  metrics - type=GAUGE, name=jvm.gc.PS-MarkSweep.time, value=1388
...

This is overly verbode in my opinion, so I made a custom logger which is logs everything on one line. You could say this is less readable, but I would use logstash anyway to filter the logs into something more practical.

In the XML file at the top, I want to use a reporter named “compact-slf4j”. Lets register a new reporter using the SPI, in a file named META-INF/services/com.ryantenney.metrics.spring.reporter.ReporterElementParser put

be.vlaanderen.awv.dc.util.metrics.CompactSlf4jReporterElementParser

We need to provide an element parser which parses the configuration:

import com.ryantenney.metrics.spring.reporter.AbstractReporterElementParser;
 
/**
 * Reporter for metrics-spring which logs more compact, all in one line instead of one line for each metric.
 */
public class CompactSlf4jReporterElementParser extends AbstractReporterElementParser {
 
    private static final String FILTER_REF = "filter-ref";
    private static final String FILTER_PATTERN = "filter";
 
    @Override
    public String getType() {
        return "compact-slf4j";
    }
 
    @Override
    protected Class<?> getBeanClass() {
        return CompactSlf4jReporterFactoryBean.class;
    }
 
    @Override
    protected void validate(ValidationContext c) {
        c.require(CompactSlf4jReporterFactoryBean.PERIOD, DURATION_STRING_REGEX, "Period is required and must be in the form '\\d+(ns|us|ms|s|m|h|d)'");
        c.optional(CompactSlf4jReporterFactoryBean.MARKER);
        c.optional(CompactSlf4jReporterFactoryBean.LOGGER);
        c.optional(CompactSlf4jReporterFactoryBean.RATE_UNIT, TIMEUNIT_STRING_REGEX, "Rate unit must be one of the enum constants from java.util.concurrent.TimeUnit");
        c.optional(CompactSlf4jReporterFactoryBean.DURATION_UNIT, TIMEUNIT_STRING_REGEX, "Duration unit must be one of the enum constants from java.util.concurrent.TimeUnit");
        c.optional(FILTER_PATTERN);
        c.optional(FILTER_REF);
        if (c.has(FILTER_PATTERN) && c.has(FILTER_REF)) {
            c.reject(FILTER_REF, "Reporter element must not specify both the 'filter' and 'filter-ref' attributes");
        }
        c.rejectUnmatchedProperties();
    }
 
}

This uses a factory bean which is defined as:

import com.ryantenney.metrics.spring.reporter.AbstractScheduledReporterFactoryBean;
import org.slf4j.LoggerFactory;
import org.slf4j.MarkerFactory;
 
import java.util.concurrent.TimeUnit;
 
/**
 * Slf4JReporterFactoryBean.
 */
public class CompactSlf4jReporterFactoryBean extends AbstractScheduledReporterFactoryBean<CompactSlf4jReporter> {
 
    /** Period attribute. */
    public static final String PERIOD = "period";
    /** Duration unit. */
    public static final String DURATION_UNIT = "duration-unit";
    /** Rate unit. */
    public static final String RATE_UNIT = "rate-unit";
    /** Marker. */
    public static final String MARKER = "marker";
    /** Logger. */
    public static final String LOGGER = "logger";
 
    @Override
    public Class<CompactSlf4jReporter> getObjectType() {
        return CompactSlf4jReporter.class;
    }
 
    @Override
    protected CompactSlf4jReporter createInstance() {
        final CompactSlf4jReporter.Builder reporter = CompactSlf4jReporter.forRegistry(getMetricRegistry());
        if (hasProperty(DURATION_UNIT)) {
            reporter.convertDurationsTo(getProperty(DURATION_UNIT, TimeUnit.class));
        }
        if (hasProperty(RATE_UNIT)) {
            reporter.convertRatesTo(getProperty(RATE_UNIT, TimeUnit.class));
        }
        reporter.filter(getMetricFilter());
        if (hasProperty(MARKER)) {
            reporter.markWith(MarkerFactory.getMarker(getProperty(MARKER)));
        }
        if (hasProperty(LOGGER)) {
            reporter.outputTo(LoggerFactory.getLogger(getProperty(LOGGER)));
        }
        return reporter.build();
    }
 
    @Override
    protected long getPeriod() {
        return convertDurationString(getProperty(PERIOD));
    }
 
}

The actual work in done in the reporter itself:

import com.codahale.metrics.Counter;
import com.codahale.metrics.Gauge;
import com.codahale.metrics.Histogram;
import com.codahale.metrics.Meter;
import com.codahale.metrics.MetricFilter;
import com.codahale.metrics.MetricRegistry;
import com.codahale.metrics.ScheduledReporter;
import com.codahale.metrics.Snapshot;
import com.codahale.metrics.Timer;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import org.slf4j.Marker;
 
import java.util.Map.Entry;
import java.util.SortedMap;
import java.util.concurrent.TimeUnit;
 
/**
 * A reporter class for logging metrics values to a SLF4J {@link Logger} periodically, similar to
 * {@link com.codahale.metrics.ConsoleReporter} or {@link com.codahale.metrics.CsvReporter}, but using the SLF4J framework instead. It also
 * supports specifying a {@link Marker} instance that can be used by custom appenders and filters
 * for the bound logging toolkit to further process metrics reports.
 */
public final class CompactSlf4jReporter extends ScheduledReporter {
 
    private final Logger logger;
    private final Marker marker;
 
    /**
     * Returns a new {@link Builder} for {@link CompactSlf4jReporter}.
     *
     * @param registry the registry to report
     * @return a {@link Builder} instance for a {@link CompactSlf4jReporter}
     */
    public static Builder forRegistry(MetricRegistry registry) {
        return new Builder(registry);
    }
 
    private CompactSlf4jReporter(MetricRegistry registry,
            Logger logger,
            Marker marker,
            TimeUnit rateUnit,
            TimeUnit durationUnit,
            MetricFilter filter) {
        super(registry, "logger-reporter", filter, rateUnit, durationUnit);
        this.logger = logger;
        this.marker = marker;
    }
 
    @Override
    public void report(SortedMap<String, Gauge> gauges,
            SortedMap<String, Counter> counters,
            SortedMap<String, Histogram> histograms,
            SortedMap<String, Meter> meters,
            SortedMap<String, Timer> timers) {
        StringBuilder data = new StringBuilder();
        for (Entry<String, Gauge> entry : gauges.entrySet()) {
            addGauge(data, entry.getKey(), entry.getValue());
        }
 
        for (Entry<String, Counter> entry : counters.entrySet()) {
            addCounter(data, entry.getKey(), entry.getValue());
        }
 
        for (Entry<String, Histogram> entry : histograms.entrySet()) {
            addHistogram(data, entry.getKey(), entry.getValue());
        }
 
        for (Entry<String, Meter> entry : meters.entrySet()) {
            addMeter(data, entry.getKey(), entry.getValue());
        }
 
        for (Entry<String, Timer> entry : timers.entrySet()) {
            addTimer(data, entry.getKey(), entry.getValue());
        }
        logger.info(marker, data.toString());
    }
 
    private void addTimer(StringBuilder data, String name, Timer timer) {
        final Snapshot snapshot = timer.getSnapshot();
        data.append(" type=timer.").append(name).append(":");
        data.append(" count=").append(timer.getCount());
        data.append(", min=").append(convertDuration(snapshot.getMin()));
        data.append(", max=").append(convertDuration(snapshot.getMax()));
        data.append(", mean=").append(convertDuration(snapshot.getMean()));
        data.append(", stdDev=").append(convertDuration(snapshot.getStdDev()));
        data.append(", median=").append(convertDuration(snapshot.getMedian()));
        data.append(", p75=").append(convertDuration(snapshot.get75thPercentile()));
        data.append(", p95=").append(convertDuration(snapshot.get95thPercentile()));
        data.append(", p98=").append(convertDuration(snapshot.get98thPercentile()));
        data.append(", p99=").append(convertDuration(snapshot.get99thPercentile()));
        data.append(", 999=").append(convertDuration(snapshot.get999thPercentile()));
        data.append(", mean_rate=").append(convertRate(timer.getMeanRate()));
        data.append(", m1=").append(convertRate(timer.getMeanRate()));
        data.append(", m5=").append(convertRate(timer.getMeanRate()));
        data.append(", m15=").append(convertRate(timer.getMeanRate()));
        data.append(", rate_unit=").append(getRateUnit());
        data.append(", duration_unit=").append(getDurationUnit());
    }
 
    private void addMeter(StringBuilder data, String name, Meter meter) {
        data.append(" type=meter.").append(name).append(":");
        data.append(" count=").append(meter.getCount());
        data.append(", mean_rate=").append(convertRate(meter.getMeanRate()));
        data.append(", m1=").append(convertRate(meter.getOneMinuteRate()));
        data.append(", m5=").append(convertRate(meter.getFiveMinuteRate()));
        data.append(", m15=").append(convertRate(meter.getFifteenMinuteRate()));
        data.append(", rate_unit=").append(getRateUnit());
    }
 
    private void addHistogram(StringBuilder data, String name, Histogram histogram) {
        final Snapshot snapshot = histogram.getSnapshot();
        data.append(" type=histogram.").append(name).append(":");
        data.append(" count=").append(histogram.getCount());
        data.append(", min=").append(snapshot.getMin());
        data.append(", max=").append(snapshot.getMax());
        data.append(", mean=").append(snapshot.getMean());
        data.append(", stdDev=").append(snapshot.getStdDev());
        data.append(", median=").append(snapshot.getMedian());
        data.append(", p75=").append(snapshot.get75thPercentile());
        data.append(", p95=").append(snapshot.get95thPercentile());
        data.append(", p98=").append(snapshot.get98thPercentile());
        data.append(", p99=").append(snapshot.get99thPercentile());
        data.append(", 999=").append(snapshot.get999thPercentile());
    }
 
    private void addCounter(StringBuilder data, String name, Counter counter) {
        data.append(" counter.").append(name).append(": ").append(counter.getCount());
    }
 
    private void addGauge(StringBuilder data, String name, Gauge gauge) {
        data.append(" gauge.").append(name).append(": ").append(gauge.getValue());
    }
 
    @Override
    protected String getRateUnit() {
        return "events/" + super.getRateUnit();
    }
 
    /**
     * A builder for {@link com.codahale.metrics.CsvReporter} instances. Defaults to logging to {@code metrics}, not
     * using a marker, converting rates to events/second, converting durations to milliseconds, and
     * not filtering metrics.
     */
    public static final class Builder {
        private final MetricRegistry registry;
        private Logger logger;
        private Marker marker;
        private TimeUnit rateUnit;
        private TimeUnit durationUnit;
        private MetricFilter filter;
 
        private Builder(MetricRegistry registry) {
            this.registry = registry;
            this.logger = LoggerFactory.getLogger("metrics");
            this.marker = null;
            this.rateUnit = TimeUnit.SECONDS;
            this.durationUnit = TimeUnit.MILLISECONDS;
            this.filter = MetricFilter.ALL;
        }
 
        /**
         * Log metrics to the given logger.
         *
         * @param logger an SLF4J {@link Logger}
         * @return {@code this}
         */
        public Builder outputTo(Logger logger) {
            this.logger = logger;
            return this;
        }
 
        /**
         * Mark all logged metrics with the given marker.
         *
         * @param marker an SLF4J {@link Marker}
         * @return {@code this}
         */
        public Builder markWith(Marker marker) {
            this.marker = marker;
            return this;
        }
 
        /**
         * Convert rates to the given time unit.
         *
         * @param rateUnit a unit of time
         * @return {@code this}
         */
        public Builder convertRatesTo(TimeUnit rateUnit) {
            this.rateUnit = rateUnit;
            return this;
        }
 
        /**
         * Convert durations to the given time unit.
         *
         * @param durationUnit a unit of time
         * @return {@code this}
         */
        public Builder convertDurationsTo(TimeUnit durationUnit) {
            this.durationUnit = durationUnit;
            return this;
        }
 
        /**
         * Only report metrics which match the given filter.
         *
         * @param filter a {@link MetricFilter}
         * @return {@code this}
         */
        public Builder filter(MetricFilter filter) {
            this.filter = filter;
            return this;
        }
 
        /**
         * Builds a {@link CompactSlf4jReporter} with the given properties.
         *
         * @return a {@link CompactSlf4jReporter}
         */
        public CompactSlf4jReporter build() {
            return new CompactSlf4jReporter(registry, logger, marker, rateUnit, durationUnit, filter);
        }
    }
 
}

OwnCloud, fixing the WebDAV warning

Posted on May 12, 2014 by justme

5,956 Comments

I had a fight with my system when trying to to a OwnCloud setup.

It was constantly saying (after a long wait when trying to open the admin page)

isWebDAVWorking: NO - Reason: [CURL] Error while making request: Connection timed out after 10001 milliseconds (error code: 28) (Sabre_DAV_Exception)

After figuring out the proper URL (https://owncloud.installation.domain/remote.php/webdav/) it dawned to me that the server me not be able to reach itself.
Indeed, adding an entry in /etc/hosts/ to assure that the domain points to 127.0.0.1 instead of the real IP address worked.

Migrating from Oracle to Postgres for a Java Hibernate application

Posted on January 23, 2014 by justme

3 Comments

For an old project which is Spring/Hibernate based, there was a need to migrate from an Oracle database to a PostgreSQL database.

The initial task was to migrate the database. I used ora2pg for this. This is a command line tool which allows you to extract your Oracle database to SQL. It was somewhat difficult to install on my Ubuntu system (because I needed the Perl Oracle client – once I got that fully installed it was a breeze, these two articles helped me a lot).

Ora2pg uses a configuration file. You need to fill in the correct for ORACLE_DSN, ORACLE_USER and ORACLE_PWD. Do not forget to also set the SCHEMA value (likely to the same value as ORACLE_USER).
To control the data which needs to be exported, you have to set the TYPE.
I first exported the table structure using “TABLE”. I then copied the result file (to prevent it from being overwritten) and then ran ora2pg again using “INSERT” as type to export the data.

Before being able to use these files, I needed to convert them to UTF-8. This was done using the command

recode ISO-8859-1..UTF8 *.sql

To create the database in Postgres I started by splitting the file with the table structure in a file which only creates the table structure itself and one which contains the constraints. I also had to extract the tail of output file with the data which contains the new values for the sequences. It was then possible to rebuild the database by first creating the structure, then inserting the data and lastly rebuilding the constraints.

psql wd_test -f output-table-structure-structure.sql
psql wd_test -f output.sql
psql wd_test -f output-table-structure-constraints.sql

To finish off I still had to add the necessary sequences (you should be able to get them though ora2pg again though I used the Hibernate generated DDL) and reset the sequences to the correct values.

Last step of the data migration was to compare the Hibernate generated DDL so see whether all constraints exist. I particularly has to add a primary key in all tables, foreign key constraints and define various unique constraints.

Then test your application.

I encountered two problems. First, there are some functions which were not available. I checked all HQL and native queries to search for functions which are used. There were two missing for this application, month and year. These had to be defined.

CREATE OR REPLACE FUNCTION MONTH(TIMESTAMP without TIME ZONE) RETURNS INTEGER
AS $$
      SELECT EXTRACT(MONTH FROM $1)::INTEGER;
$$ LANGUAGE SQL IMMUTABLE;
 
CREATE OR REPLACE FUNCTION MONTH(TIMESTAMP WITH TIME ZONE) RETURNS INTEGER
AS $$
      SELECT EXTRACT(MONTH FROM $1)::INTEGER;
$$ LANGUAGE SQL STABLE;
 
CREATE OR REPLACE FUNCTION MONTH(DATE) RETURNS INTEGER
AS $$
      SELECT EXTRACT(MONTH FROM $1)::INTEGER;
$$ LANGUAGE SQL IMMUTABLE;
 
 
CREATE OR REPLACE FUNCTION YEAR(TIMESTAMP without TIME ZONE) RETURNS INTEGER
AS $$
      SELECT EXTRACT(YEAR FROM $1)::INTEGER;
$$ LANGUAGE SQL IMMUTABLE;
 
CREATE OR REPLACE FUNCTION YEAR(TIMESTAMP WITH TIME ZONE) RETURNS INTEGER
AS $$
      SELECT EXTRACT(YEAR FROM $1)::INTEGER;
$$ LANGUAGE SQL STABLE;
 
CREATE OR REPLACE FUNCTION YEAR(DATE) RETURNS INTEGER
AS $$
      SELECT EXTRACT(YEAR FROM $1)::INTEGER;
$$ LANGUAGE SQL IMMUTABLE;

Lastly, there were count queries which had an order defined on them. Typically the query was built using generic code and either executed normally or using a count projection. This works perfectly in Oracle but Postgres complains saying

column “tableName.fieldName” must appear in the GROUP BY clause or be used in an aggregate function

Fixing the code for this seemed non-trivial and possible cause of bugs, so I introduced “patch” code which removes the order from the query and is called before applying the count projection.

public final class PgCompatibility {
 
    private static final Logger LOG = LoggerFactory.getLogger(PgCompatibility.class);
 
    private PgCompatibility() {
        // hide constructor
    }
 
    /**
     * Criteria from which the order needs to be removed.
     * <p/>
     * On queries like "select count(*) from TD_MAANDPRESTATIE order by D_EERSTE_KALENDERDAG asc" the order is
     * irrelevant. Oracle seems to recognize this while Postgres gives an error like
     * "column "d_eerste_kalenderdag" must appear in the GROUP BY clause or be used in an aggregate function"
     *
     * @param criteria criteria from which the order needs to be removed if possible
     */
    public static void removeOrder(Criteria criteria) {
        if (criteria instanceof CriteriaImpl) {
            try {
                Field orderEntries = CriteriaImpl.class.getDeclaredField("orderEntries");
                makeAccessible(orderEntries);
                ((List) orderEntries.get(criteria)).clear();
            } catch (NoSuchFieldException nsfe) {
                LOG.error("Cannot find field.", nsfe);
            } catch (IllegalAccessException iae) {
                LOG.error("Cannot access field.", iae);
            }
        }
    }
 
    /**
     * Make the given field accessible, explicitly setting it accessible if necessary.
     * The setAccessible(true) method is only called when actually necessary, to avoid unnecessary
     * conflicts with a JVM SecurityManager (if active).
     * <p/>
     * This method is borrowed from Spring's ReflectionUtil class.
     *
     * @param field the field to make accessible
     * @see java.lang.reflect.Field#setAccessible
     */
    public static void makeAccessible(Field field) {
        if ((!Modifier.isPublic(field.getModifiers()) || !Modifier.isPublic(field.getDeclaringClass().getModifiers()) ||
                Modifier.isFinal(field.getModifiers())) && !field.isAccessible()) {
            field.setAccessible(true);
        }
    }
}

Presto, migration worked.

Logging JVM and OS metrics in a spring application

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OwnCloud, fixing the WebDAV warning

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Migrating from Oracle to Postgres for a Java Hibernate application

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