ILoggingEvent interface assumes that getTimeStamp() is in milliseconds.

Elasticsearch @timestamp resolution is in milliseconds too, see https://github.com/elastic/elasticsearch/issues/10005

As workaround people store second fraction in separate field in ES.

When sorting by @timestamp in ES events are ordered randomly within millisecond. In contrast writing to file at any precision preserves ordering.

Is it possible to increase timestamp resolution?

With current hardware nanosecond resolution is pretty good.

DETAILS:

We collect log events into Elasticsearch with project that writes timestamp via:

https://github.com/internetitem/logback-elasticsearch-appender/blob/master/src/main/java/com/internetitem/logback/elasticsearch/AbstractElasticsearchPublisher.java

   protected static String getTimestamp(long timestamp) {
       return DATE_FORMAT.get().format(new Date(timestamp));
   }

https://github.com/internetitem/logback-elasticsearch-appender/blob/master/src/main/java/com/internetitem/logback/elasticsearch/ClassicElasticsearchPublisher.java

    public class ClassicElasticsearchPublisher extends AbstractElasticsearchPublisher<ILoggingEvent> {

        @Override
        protected void serializeCommonFields(JsonGenerator gen, ILoggingEvent event) throws IOException {
            gen.writeObjectField("@timestamp", getTimestamp(event.getTimeStamp()));

Only by changing ILoggingEvent or by providing alternative interface it would be possible to preserve timestamp in better resolution.