SQL Server – Technical Meaning of ‘Bulk’ in Bulk-Logged Recovery Model

recovery-modelsql serverterminology

With this model there are certain bulk operations such as BULK INSERT, CREATE INDEX, SELECT INTO, etc… that are not fully logged in the transaction log and therefore do not take as much space in the transaction log.

What is the technical meaning of "Bulk" in the "Bulk-Logged Recovery Model"? I need clarity on what-all is classified as bulk please. Is every bulk insert, create index, select into classified as bulk or does it depend on volume of data involved?

As I understand, the Bulk-Logged Recovery Model doesn't fully log the bulk transactions. Then why is it named like this?

Best Answer

As I understand, the Bulk-Logged Recovery Model doesn't fully log the bulk transactions. Then why is it named like this?

Without an answer from the folks that actually named this recovery model, we can only guess about the name. But it seems to me like "bulk-logged" means something similar to "buying in bulk."

You can buy a single steak every day at the grocery store for one price. OR, you could buy in bulk, and get a whole month's supply of steaks for significantly cheaper (per steak).

Similarly, you can log every single action and its data (Full Recovery model). OR, you can log the transactions in bulk (just the page allocations), for significant "savings" in how much information needs to be written to the transaction log.

Related Solutions

Sql-server – Why “Select * into targettable from sourcetable “ is faster than “insert into targettable select * from sourcetable

A couple of ideas/theories:

SELECT INTO... lets the RDBMS determine sort order based on order of your original table. If you insert into an existing table, there may be a sort needed to match a clustered or nonclustered index(es).

No Indexes - when you SELECT INTO... the RDBMS knows for certain there are no pre-existing indexes to update.

No Contention - since the table you are inserting into does not exist, SQL Server doesn't need to worry about row-level locking or contention handling. Nothing else can reference the table you create since it doesn't exist.

All that being said, there are other ways to insert into a table very quickly.

Make sure your clustered index keys match when possible. This means there is no on-the-fly sorting
Disable all non-clustered indexes. Self-explanatory.
Set recovery mode to simple and trace flag 610 to ON. Use the TABLOCK hint on your target table and NOLOCK hint on your source table.

For example, assume tablea and tableb have the same clustered index:

INSERT INTO TableB WITH (TABLOCK)
SELECT <Columns>
FROM TableA WITH (NOLOCK)

In my experience this is faster than using SELECT INTO... and then creating the clustered index afterwards. Please note this can also work on a table that already has data in it which is a much more useful scenario.

EDIT:

Here's a fantastically detailed whitepaper from MS for data load performance in Sql Server 2008.

Sql-server – Is it good idea to change Simple Recover Model into Bulk-Logged on ETL system

If you log grows on ETL in simple mode it means your inserts are not minimally logged. The requirements for minimal logging are described in Operations That Can Be Minimally Logged and Prerequisites for Minimal Logging in Bulk Import:

Minimal logging requires that the target [of a INSERT BULK operation] table meets the following conditions:

The table is not being replicated.

Table locking is specified (using TABLOCK).

The Data Loading Performance Guide also mentions the TF 610 effects and how it affects minimal logging.

Best Answer

Related Solutions

Sql-server – Why “Select * into targettable from sourcetable “ is faster than “insert into targettable select * from sourcetable

Sql-server – Is it good idea to change Simple Recover Model into Bulk-Logged on ETL system

Related Question