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Revision 3285

Added by Aaron Marcuse-Kubitza over 12 years ago

sql_io.py: put_table(): mk_main_select(): Turned off unnecessary ORDER BY to avoid sorting the entire table every time it's used. (PostgreSQL has no concept of reordering a table and re-using that ordering, so it just re-sorts the table each time. Index scans on the pkey do not appear to be used in practice, according to EXPLAIN results from live imports.) Document that we instead assume that identical SELECT queries retrieve rows in the same order.

View differences:

lib/sql_io.py
316 316 
    def mk_main_select(joins, cols):
317 317 
        conds_ = [(sql_gen.with_table(k, insert_in_table), v) for k, v in conds]
318 318 
        return sql.mk_select(db, joins, cols, conds_, limit=limit_ref[0],
319 
            start=0)
319 
            order_by=None, start=0)
320 320
321 321 
    exc_strs = set()
322 322 
    def log_exc(e):
......
453 453 
        sql.add_row_num(db, insert_out_pkeys) # for joining with input pkeys
454 454
455 455 
        log_debug('Getting input table pkeys of inserted rows')
456 
        # Note that mk_main_select() does not use ORDER BY. Instead, assume that
457 
        # since the SELECT query is identical to the one used in INSERT SELECT,
458 
        # its rows will be retrieved in the same order.
456 459 
        sql.run_query_into(db, mk_main_select(input_joins, [in_pkey]),
457 460 
            into=insert_in_pkeys)
458 461 
        sql.add_row_num(db, insert_in_pkeys) # for joining with output pkeys

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