A strong technical review on Oracle Bigfile Tablespace

 A strong technical review on Oracle Bigfile Tablespace
and exploring the challenges & Concerns for DBAs

Bigfile Tablespaces in Oracle:

Oracle Database enables the creation of bigfile tablespaces.

A bigfile tablespace consists of a single data or temporary file which can be up to 128 TB. The use of bigfile tablespaces can significantly reduce the number of data files for your database. Oracle Database supports parallel RMAN backup and restore on single data files.

Consequently, there is no disadvantage to using bigfile tablespaces and you may choose to use bigfile tablespaces to significantly reduce the number of data and temporary files.

v  File allocation is a serial process. If you use automatic allocation for your tables and automatically extensible data files, then a large data load can be impacted by the amount of time it takes to extend the file, regardless of whether you use bigfile tablespaces. However, if you preallocate data files and you use multiple data files, then multiple processes are spawned to add data files concurrently.

An Oracle Bigfile tablespace is a special tablespace that contains only one extremely large datafile (up to 128 TB), offering benefits like significantly increased storage capacity, simplified management by reducing the number of datafiles, and datafile transparency where operations can be performed on the tablespace rather than individual datafiles. Bigfile tablespaces are ideal for large databases and work best with technologies like Oracle ASM or other logical volume managers that support dynamic volume resizing.

Benefits of Bigfile Tablespaces

• Increased Storage Capacity:

By using a single, very large datafile instead of many smaller ones, bigfile tablespaces can dramatically increase the maximum storage capacity of an Oracle Database. 

• Simplified Management:

With only one file to manage per tablespace, database administration becomes simpler, especially for ultra-large databases. 

• Datafile Transparency:

You can perform operations like backup, restore, and resize on the entire tablespace, rather than having to manage individual datafiles. 

·         Reduced Control File and SGA Overhead:

Bigfile tablespaces reduce the amount of information the database needs to track for datafiles, decreasing the size of the control file and the space required in the System Global Area (SGA). 

• Parallel RMAN Backup and Restore:

Oracle supports parallel operations for RMAN (Recovery Manager) backup and restore on the single, large datafile of a bigfile tablespace. 

Considerations

• Compatibility with Logical Volume Managers:

Bigfile tablespaces are designed to be used with systems like Oracle ASM or other logical volume managers that can provide dynamically extensible logical volumes, striping, and RAID capabilities. 

• Multisection Backups:

For very large bigfile tablespaces, the ability to create multisection backups using multiple channels to read sections of the single large datafile can improve performance. 

• Default Behavior in Recent Versions:

In recent Oracle versions (such as Oracle 23ai), bigfile tablespaces are often the default for newly created tablespaces, simplifying management of large databases. 

In essence, bigfile tablespaces are a key feature for handling very large amounts of data efficiently by reducing the complexity of file management and increasing the potential scale of Oracle databases. 

 

Oracle Bigfile VS Small file Tablespace

As an Oracle DBA, usually you select which model in Production env? 

Do you have concerns about the Bigfile model?

In Oracle, Bigfile Tablespace (BFTS) vs Smallfile Tablespace (SFTS) is mostly a management and architecture decision, not a raw performance feature.

Let’s break it down:

Advantages of Bigfile Tablespace

• Fewer Datafiles → Easier management in databases with thousands of tablespaces (no need to manage hundreds of small files).
• Supports very large databases → One datafile can go up to 128TB (depending on block size and OS).
• ASM / OMF integration → Works best with Automatic Storage Management (ASM) or Oracle Managed Files, where the file system limits (e.g., max files per volume) might be a concern.
• Online resize → You can resize a single file easily instead of managing multiple small ones.

 

 Potential Disadvantages / Challenges:

1. Backup & Recovery

• With RMAN, a single very large file means if corruption hits the file header or file gets damaged, you deal with the entire multi-terabyte file, not just a 10–50 GB chunk although Section Size parameter in RMAN can be used.
• Incremental backups mitigate this (RMAN tracks block changes), but initial backups and restores are still heavy.

2. I/O Performance Concerns

• Oracle accesses blocks, not files → so in theory, no performance penalty.
• But in practice, on some storage subsystems, very large files may lead to:
• OS-level limits (metadata, extent maps).
• Suboptimal striping on some legacy filesystems.
• Modern ASM / SAN / Exadata generally eliminates this concern.

3. Tablespace Operations

• If you need to move a bigfile tablespace (e.g., to another storage system), you have to move a huge file in one piece. With smallfiles, you can parallelize movement of multiple files.

 

4. Compatibility / Administration

• Some 3rd-party tools (older backup agents, monitoring, etc.) don’t handle multi-terabyte single files well.
• DBA "comfort level" → many DBAs prefer multiple files for granularity and flexibility.

5. Flashback / Recovery Time

• During recovery, handling one huge file may be slower than parallel recovery of multiple smaller datafiles.
• If corruption affects one portion of a BFTS, you may be forced to recover the entire file.

 Practical Considerations:

• On Exadata / ASM / OMF → Bigfile is safe and often recommended, since the storage layer takes care of striping, balancing, and performance.
• On traditional file systems or non-ASM storage → many DBAs stick with Smallfiles for backup/recovery granularity and manageability.
• Hybrid approach → use BFTS for large objects (e.g., data warehouse fact tables, staging) and SFTS for OLTP / critical smaller workloads.

Rule of Thumb:

• OLTP systems with mixed workloads → Smallfile may still be better for more granular backup and restore, but the performance impact such as I/O is almost the same in both.
• DW / DWH / Exadata / ASM-managed databases → Bigfile is fine (and often preferred).
• If unsure → default to Smallfile unless you have a strong storage/management reason to choose Bigfile.

 

Are you have any other concerns about using Bigfile tablespace:

Oracle Database does not treat Bigfile Tablespaces differently from Smallfile Tablespaces in terms of I/O performance.

• Oracle reads and writes at the block level, not at the file level.

·         Whether those blocks live in fileA.dbf (100 GB smallfile) or in fileB.dbf (5 TB bigfile) makes no difference to the optimizer, buffer cache, or physical I/O operations.

• The extent and segment management inside the tablespace is identical — same bitmap, same freelists, same algorithms.

When There Is No Performance Issue

• Oracle kernel I/O path → No penalty. The database engine issues I/O requests per block/extent.
• ASM / Exadata / modern SAN → These automatically stripe data across disks, so even one bigfile gets spread evenly.
• RMAN incremental backups → Only changed blocks are backed up, regardless of file size.

Where Performance Problems Might Appear:

Not because of Oracle, but because of the underlying OS / storage:

• Legacy filesystems → Some OSs have inefficient file extent maps when file size is multi-TB. This can slow metadata operations (open, extend, checkpoint scanning).
• Backup / restore throughput → Copying or recovering one 5 TB file might be slower than handling 50×100 GB files in parallel.
• Corruption recovery granularity → With smallfiles, you might restore only one 100 GB file; with a bigfile, you must restore the entire multi-TB file, even if only a tiny portion was affected.

Bottom line for DBAs:

• I/O performance is the same → Oracle does not penalize Bigfile vs Smallfile.
• The concern is not I/O speed but operational flexibility (backup, recovery, corruption handling, file movement).
• That’s why many DBAs feel safer with Smallfiles, even though the engine performs equally well.

 Datafile Limits with Smallfile Tablespaces

• Each Smallfile Tablespace (SFTS) can have up to 1,022 datafiles (on most platforms).
• Each datafile can be up to 32 GB × block size (so with 8K block size → ~32 TB per tablespace).
• If your database grows very large, you may end up with thousands of datafiles across all tablespaces.

This stresses:

• Control file size (Oracle must track all file headers).
• SPFILE/PFILE parameters (e.g., DB_FILES), which sets the upper limit of total datafiles the DB can open.
• Startup overhead (Oracle must scan all file headers).
• Backup/restore catalog size (RMAN has to track each file individually).

 

Bigfile Tablespaces Avoid This

• A Bigfile Tablespace has only one datafile.
• That file can grow up to 128 TB (8K block size with 32-bit file header) or more with 64-bit headers.
• DB_FILES limit becomes less relevant, since you need only a handful of very large files instead of thousands of small ones.

 

 Trade-off:

• Smallfiles → more granularity in recovery, but risk of hitting DB_FILES and control file bloat.
• Bigfiles → reduce file count dramatically, but one file can be “too big to fail” (restore/repair impact).

 

• If using ASM or Exadata → BFTS is often preferred, since storage spreads I/O automatically but backup recovery and Recovery time objective (RTO) can lead to use Smallfile.
• If using traditional file systems → be mindful of OS file size limits; sometimes many smallfiles are safer.
• For very large databases (VLDBs) → Bigfile is a practical solution to avoid DB_FILES hitting the ceiling.
• DB_FILES parameter → you can increase it (up to 65,533 depending on platform), but this increases controlfile size and memory usage.
• From Oracle database 26ai onward we can use the DBMS_SPACE package to shrink a bigfile tablespace to reclaim unused space.

 

Alireza Kamrani

Oracle Solutions Advisor, ACE Pro