Question

I have a multithreaded process which inserts several records into a single table. The inserts are performed in a stored procedure, with the sequence being generated INTO a variable, and that variable is later used inside of an INSERT.

Given that I’m not doing mysequence.nextval inside the INSERT itself, it makes me think that it is possible for two concurrent processes to grab a sequence in one order, then do the inserts in the reverse order. If this is the case, then the sequence numbers will not reflect the true order of insertion.

I also record the sysdate in a DATE column for each of my inserts, but I’ve noticed that often times the dates for two records match and I need to sort by the sequence number to break the tie. But given the previous issue, this doesn’t seem to guarantee the actual insert order.

How can I determine the absolute order of insertion into the database?

Answer 1

DATE datatypes only go to seconds, whereas TIMESTAMP goes to milliseconds. Would that address the problem?

According to Oracle’s docs:

TIMESTAMP: Year, month, and day values
of date, as well as hour, minute, and
second values of time, where
fractional_seconds_precision is the
number of digits in the fractional
part of the SECOND datetime field.
Accepted values of
fractional_seconds_precision are 0 to
9. The default is 6. The default format is determined explicitly by the
NLS_DATE_FORMAT parameter or
implicitly by the NLS_TERRITORY
parameter. The sizes varies from 7 to
11 bytes, depending on the precision.
This datatype contains the datetime
fields YEAR, MONTH, DAY, HOUR, MINUTE,
and SECOND. It contains fractional
seconds but does not have a time zone.

Whereas date does not:

DATE: Valid date range from January 1,
4712 BC to December 31, 9999 AD. The
default format is determined
explicitly by the NLS_DATE_FORMAT
parameter or implicitly by the
NLS_TERRITORY parameter. The size is
fixed at 7 bytes. This datatype
contains the datetime fields YEAR,
MONTH, DAY, HOUR, MINUTE, and SECOND.
It does not have fractional seconds or
a time zone.

Of course, having said that, I am not sure why it matters when the records were written, but that is a way that might solve your problem.