SOLVED: Re: HELP: How to tame the 8.3.x JDBC driver with a biq guery result set

[Dave Crooke <dcrooke@xxxxxxxxx>]

When a connection is used for both reading and writing, a commit() also destroys any open cursors. Simple workaround - use two connections.

See full discussion on JDBC list.

Cheers
Dave

On Thu, Apr 15, 2010 at 3:01 PM, Dave Crooke <dcrooke@xxxxxxxxx> wrote:

I have followed the instructions below to no avail .... any thoughts?

http://jdbc.postgresql.org/documentation/83/query.html#query-with-cursor

This is what happens when I reduce the fetch_size to 50 ... stops after about 950msec and 120 fetches (6k rows) ....

13:59:56,054 [PerfDataMigrator] ERROR com.hyper9.storage.sample.persistence.PersistenceManager:3216 - Unexpected error while migrating sample data: 6000

org.postgresql.util.PSQLException: ERROR: portal "C_14" does not exist

    at org.postgresql.core.v3.QueryExecutorImpl.receiveErrorResponse(QueryExecutorImpl.java:1592)
    at org.postgresql.core.v3.QueryExecutorImpl.processResults(QueryExecutorImpl.java:1327)
    at org.postgresql.core.v3.QueryExecutorImpl.fetch(QueryExecutorImpl.java:1527)
    at org.postgresql.jdbc2.AbstractJdbc2ResultSet.next(AbstractJdbc2ResultSet.java:1843)

    at org.apache.commons.dbcp.DelegatingResultSet.next(DelegatingResultSet.java:169)
    at org.apache.commons.dbcp.DelegatingResultSet.next(DelegatingResultSet.java:169)
    at com.hyper9.storage.sample.persistence.PersistenceManager$Migrator.run(PersistenceManager.java:3156)
    at java.lang.Thread.run(Thread.java:619)

Cheers
Dave

On Thu, Apr 15, 2010 at 2:42 PM, Dave Crooke <dcrooke@xxxxxxxxx> wrote:

Hey folks

I am trying to do a full table scan on a large table from Java, using a straightforward "select * from foo". I've run into these problems:

1. By default, the PG JDBC driver attempts to suck the entire result set into RAM, resulting in java.lang.OutOfMemoryError ... this is not cool, in fact I consider it a serious bug (even MySQL gets this right ;-) I am only testing with a 9GB result set, but production needs to scale to 200GB or more, so throwing hardware at is is not feasible.

2. I tried using the official taming method, namely java.sql.Statement.setFetchSize(1000) and this makes it blow up entirely with an error I have no context for, as follows (the number C_10 varies, e.g. C_12 last time) ...

org.postgresql.util.PSQLException: ERROR: portal "C_10" does not exist
    at org.postgresql.core.v3.QueryExecutorImpl.receiveErrorResponse(QueryExecutorImpl.java:1592)
    at org.postgresql.core.v3.QueryExecutorImpl.processResults(QueryExecutorImpl.java:1327)
    at org.postgresql.core.v3.QueryExecutorImpl.fetch(QueryExecutorImpl.java:1527)
    at org.postgresql.jdbc2.AbstractJdbc2ResultSet.next(AbstractJdbc2ResultSet.java:1843)

This is definitely a bug :-)


Is there a known workaround for this ... will updating to a newer version of the driver fix this?

Is there a magic incation of JDBC calls that will tame it?

Can I cast the objects to PG specific types and access a hidden API to turn off this behaviour?

If the only workaround is to explicitly create a cursor in PG, is there a good example of how to do this from Java?

Cheers
Dave