Does TRUNCATE TABLE grows up transaction log?

Question

I have read that one of the differences between DELETE and TRUNCATE TABLE in Sql is the TRUNCATE operation cannot be rolled back and no triggers will be fired (as written in this site for example) :

QUESTION: Does this mean that when I TRUNcATE TABLE that is containing millions of records, I should not be effecting the transaction log file -that is transaction log file should not grow up in the time of truncating-, am I correct?

Answer 1

In MS SQL Server (Books Online)

Compared to the DELETE statement, TRUNCATE TABLE has the following advantages:

• Less transaction log space is used.

  The DELETE statement removes rows one at a time and records an entry in the transaction log for each deleted row. TRUNCATE TABLE removes the data by deallocating the data pages used to store the table data and records only the page deallocations in the transaction log.

• Fewer locks are typically used.

  When the DELETE statement is executed using a row lock, each row in the table is locked for deletion. TRUNCATE TABLE always locks the table (including a schema (SCH-M) lock) and page but not each row.

• Without exception, zero pages are left in the table.

  After a DELETE statement is executed, the table can still contain empty pages. For example, empty pages in a heap cannot be deallocated without at least an exclusive (LCK_M_X) table lock. If the delete operation does not use a table lock, the table (heap) will contain many empty pages. For indexes, the delete operation can leave empty pages behind, although these pages will be deallocated quickly by a background cleanup process.

  TRUNCATE TABLE removes all rows from a table, but the table structure and its columns, constraints, indexes, and so on remain. To remove the table definition in addition to its data, use the DROP TABLE statement.

  If the table contains an identity column, the counter for that column is reset to the seed value defined for the column. If no seed was defined, the default value 1 is used. To retain the identity counter, use DELETE instead.

From: http://msdn.microsoft.com/en-us/library/ms177570.aspx

To the original question:

Technically TRUNCATE is deallocating the data pages from the table, effectively removing all records from it. This action in theory can be rolled back until none of the data pages are being re-used. The information on the deallocated pages are not removed, they are still available in the data file. These deallocated pages in the data file can be re-used (allocated to another table for example) and the data on them can be overwritten.

The transaction log contains the list of pages (in SQL Server) being deallocated from the table during TRUNCATE, but this list is much shorter than the list of all records, therefore the transaction log will not grow to the same extent.

Depending on the implementation of transactions and TRUNCATE on different RDBMS it can be possible to do a rollback within a transaction. Sometimes it is possible to do a 'rollback' (restore the table) after the transaction is committed, if the data on the pages are still intact and all information is available, but that is some black magic and usually not supported directly by the RDBMS.