org.firebirdsql.jdbc.FBSQLException: GDS Exception. 335544336. deadlock update conflicts with concurrent update

Эта хрень возникает из за того что два потока пытаются одновременно изменить поля одной и той же ентити. Вот что пишут про это
 http://www.firebirdfaq.org/faq151/ ,
http://edn.embarcadero.com/article/30213.

В целом есть два способа это побороть

1)В коде добавить синхронизацию

2)Разобраться с изоляцией транзакций.
Подробнее:
http://ru.wikipedia.org/wiki/Уровни_изолированности_транзакций
для хибернэйта они задаются параметром  hibernate.connection.isolation в пропертях,
значения описаны в java.sql.Connection:
Наверняка:
для hibernate, в пропертях прописать: hibernate.connection.isolation=8

Выдержки из java.sql.Connection:

    /**
     * A constant indicating that transactions are not supported.
     */
    int TRANSACTION_NONE     = 0;

    /**
     * A constant indicating that
     * dirty reads, non-repeatable reads and phantom reads can occur.
     * This level allows a row changed by one transaction to be read
     * by another transaction before any changes in that row have been
     * committed (a "dirty read").  If any of the changes are rolled back,
     * the second transaction will have retrieved an invalid row.
     */
    int TRANSACTION_READ_UNCOMMITTED = 1;

    /**
     * A constant indicating that
     * dirty reads are prevented; non-repeatable reads and phantom
     * reads can occur.  This level only prohibits a transaction
     * from reading a row with uncommitted changes in it.
     */
    int TRANSACTION_READ_COMMITTED   = 2;

    /**
     * A constant indicating that
     * dirty reads and non-repeatable reads are prevented; phantom
     * reads can occur.  This level prohibits a transaction from
     * reading a row with uncommitted changes in it, and it also
     * prohibits the situation where one transaction reads a row,
     * a second transaction alters the row, and the first transaction
     * rereads the row, getting different values the second time
     * (a "non-repeatable read").
     */
    int TRANSACTION_REPEATABLE_READ  = 4;

    /**
     * A constant indicating that
     * dirty reads, non-repeatable reads and phantom reads are prevented.
     * This level includes the prohibitions in
     * TRANSACTION_REPEATABLE_READ and further prohibits the
     * situation where one transaction reads all rows that satisfy
     * a WHERE condition, a second transaction inserts a row that
     * satisfies that WHERE condition, and the first transaction
     * rereads for the same condition, retrieving the additional
     * "phantom" row in the second read.
     */
    int TRANSACTION_SERIALIZABLE     = 8;