Conventional path load (the default) uses the SQL INSERT statement and a bind array buffer to load data into database tables. This method is used by all Oracle tools and applications.

When SQL*Loader performs a conventional path load, it competes equally with all other processes for buffer resources. This can slow the load significantly. Extra overhead is added as SQL statements are generated, passed to Oracle, and executed.

The Oracle database looks for partially filled blocks and attempts to fill them on each insert. Although appropriate during normal use, this can slow bulk loads dramatically.

Instead of filling a bind array buffer and passing it to the Oracle database with a SQL INSERT statement, a direct path load uses the direct path API to pass the data to be loaded to the load engine in the server. The load engine builds a column array structure from the data passed to it.

The direct path load engine uses the column array structure to format Oracle data blocks and build index keys. The newly formatted database blocks are written directly to the database (multiple blocks per I/O request using asynchronous writes if the host platform supports asynchronous I/O).

Internally, multiple buffers are used for the formatted blocks. While one buffer is being filled, one or more buffers are being written if asynchronous I/O is available on the host platform. Overlapping computation with I/O increases load performance.

alter session enable parallel dml;
insert /*+ parallel (a,8)*/ into a
select /*+ parallel (b,8) * from b;

Ну вот в том-то и вопрос: есть в файле записи 1,2,3...10. Загрузка идёт с DEGREE_OF_PARALLELISM=2, то есть в две сессии. Будут записи 1,2,3,4,5 вставлены в одной сессии, а 6,7,8,9,10 - в другой? Или в одной сессии будут 1,3,5,7,9, а в другой 2,4,6,8,10?

WHERE MOD(ORA_HASH(:B1),< DEGREE_OF_PARALLELISM >) = 0 (1,2,3...N)

На первый взгляд звучит неплохо, но меня терзает смутное сомнение: если коммит первой сессии прошёл, а второй - обломался по любой причине, мы получаем базу в которую загрузилась только половина записей из файла и без хрустального шара не угадать каких записей не хватает?..