createDatabaseIfNotExists throws "org.ektorp.DbAccessException: A database with path X already exists"

[huxi]

This happens pretty random and I suspect that the database is under load...

Exception in thread "main" org.ektorp.DbAccessException: A database with path /string_list_nl/ already exists
        at org.ektorp.impl.StdCouchDbInstance.createDatabase(StdCouchDbInstance.java:51)
        at org.ektorp.impl.StdCouchDbInstance.createDatabase(StdCouchDbInstance.java:46)
        at org.ektorp.impl.StdCouchDbConnector.createDatabaseIfNotExists(StdCouchDbConnector.java:406)
        at org.ektorp.support.CouchDbRepositorySupport.<init>(CouchDbRepositorySupport.java:53)
        at org.ektorp.support.CouchDbRepositorySupport.<init>(CouchDbRepositorySupport.java:44)

Using ektorp 1.4.1 with couchdb 1.5.0.

Code looks like this:

@Views({
    @View(name = "all", file="/couch/list/allView.json"),
    @View(name = "tag_counts", file="/couch/list/listEntryCounts.json")
})
public class StringListCouchDbRepository
        extends CouchDbRepositorySupport<StringList> {

    public StringListCouchDbRepository(CouchDbConnector db) {
        super(StringList.class, db);
        initStandardDesignDocument();
    }
    // [..]
}

[huxi]

Additional info about dependencies:

[INFO] +- org.ektorp:org.ektorp.spring:jar:1.4.1:runtime
[INFO] |  \- org.aspectj:aspectjweaver:jar:1.7.4:runtime (version managed from 1.6.9)

[INFO] |  +- org.ektorp:org.ektorp:jar:1.4.1:compile
[INFO] |  |  +- org.apache.httpcomponents:httpclient:jar:4.3.2:compile (version managed from 4.2.5)
[INFO] |  |  |  +- org.apache.httpcomponents:httpcore:jar:4.3.1:compile
[INFO] |  |  |  \- commons-codec:commons-codec:jar:1.7:compile (version managed from 1.6)
[INFO] |  |  +- org.apache.httpcomponents:httpclient-cache:jar:4.3.2:compile (version managed from 4.2.5)
[INFO] |  |  +- commons-io:commons-io:jar:2.4:compile (version managed from 2.0.1)
[INFO] |  |  \- com.fasterxml.jackson.core:jackson-annotations:jar:2.3.1:compile (version managed from 2.2.2)

[helun]

Do you create databases on the fly?
It looks like there might be multiple nodes in your system that is trying to create the same db at the same time.

[huxi]

The databases are all existing already and the exception is happening really randomly. I'm executing similar actions on a bunch of databases of this type where only the dbName is changed. But those are all fresh instances that are sharing the same CouchDbInstance. Executing those actions multiple times results in the exception above with different dbNames. Databases that worked on a previous run would suddenly throw the exception and vice versa.

The code initializing our repository looks like this:

    private void setCouchDbInstance(CouchDbInstance couchDbInstance)
    {
        this.couchDbInstance = couchDbInstance;
        StdCouchDbConnector db = new StdCouchDbConnector(dbName, couchDbInstance, new ResourceObjectMapperFactory());
        repo=new StringListCouchDbRepository(db);
    }

    private static class ResourceObjectMapperFactory
        implements ObjectMapperFactory
    {
        public ObjectMapper createObjectMapper()
        {
            ObjectMapper result = new ObjectMapper();
            result.configure(SerializationFeature.WRITE_DATES_AS_TIMESTAMPS, false);
            result.setDateFormat(new ISO8601DateFormat());
            result.registerModule(new StringListModule());
            result.registerModule(new AfterburnerModule());
            return result;
        }

        public ObjectMapper createObjectMapper(CouchDbConnector connector)
        {
            return createObjectMapper();
        }
    }

And the configuration of the CouchDbInstance looks like this:

<bean name="couchDb" class="org.ektorp.impl.StdCouchDbInstance">
    <constructor-arg>
        <bean class="org.ektorp.spring.HttpClientFactoryBean" p:username="xxx" p:password="yyy" p:port="5984">
            <property name="host" value="zzz"/>
            <property name="autoUpdateViewOnChange" value="true"/>
        </bean>
    </constructor-arg>
</bean>

I suspect that our CouchDB was barfing under heavy load and returned some error (probably 500) which is interpreted as "does not exist" in StdCouchDbInstance

    public boolean checkIfDbExists(DbPath db) {
        return restTemplate.head(db.getPath(), new StdResponseHandler<Boolean>() {
        @Override
        public Boolean error(HttpResponse hr) {
            return false;
        }
        @Override
        public Boolean success(HttpResponse hr) throws Exception {
            return true;
        }
        });
    }

I'd suggest throwing a DbAccessException if hr.getCode() returns an unexpected value in error(...) instead of just returning false in any error case. That exception should include the message from the server. I highly suspect that an error should be thrown in my case (because the CouchDB was acting funky, returning 500 in case of some other calls) but the message that is currently produced is wrong and misleading.

[huxi]

I can confirm that the couchdb is returning 500 in those cases (for unrelated reasons). This causes checkIfDbExists(..) to erroneously return false.

[huxi]

I've sent #186 to fix this. The tests are working (after fixing mock assumptions according to the new implementation) but I didn't check it against a real CouchDB since I don't know if/how I could do that in your build.

Let me know if anything is wrong.