Re: Transaction atomicity

> I have a question about a simple code that should automatically insert
a
> record in a table. The primary key for this record is automatically
> generated during the INSERT statement, as the max value plus one.
>
> The (simplified, since the real number of fields is 5) code is:
>
> final String query = "INTO table (docId,seqNr) " +
>         "VALUES (?, (SELECT 1 + coalesce (max(seqNr), 0) "+
>         "FROM table " +
>         "WHERE seqNr BETWEEN 0 AND (9223372036854775807-1) ))";
> Connection conn=daof.getConnection();
> try {
>     conn.setAutoCommit(true);
>     PrepararedStatemen st = conn.prepareStatement(query);
>     st.setString(1,'myDocId');
>     st.executeUpdate();
>     conn.close();
> }
> catch (SQLException e) {
>     try { conn.close(); } catch (SQLException ee) {}
>     throw e;
> }
>
> I then create Runtime.getRuntime().availableProcessors() threads that
> create a DataSource and start executing that code in parallel. What
> happens is that I get many DUPLICATE KEY errors. I thought that in
> AutoCommit all insert are supposed to be serialized, so they should
> create a seqNr different since MAX(seqNr) is different at each call.
>
> Is my reasoning correct? Or is it a different problem, maybe with jdbc
> or postgresql?

Does the behaviour change if you set the prepare threshold of
the statement to 0?

Yours,
Laurenz Albe