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Deciphering the SQL Fix Recovery Model

  • Karen Anthony 
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Recovery models are database configurations that determine the nature of backup that a person performs and provide the chance of restoring data and recovering it from failure. The model decides the maintenance of the database’s transaction log as it reflects information modifications in a sequence. You may use it later on for database restore operations.

Different categories of the recovery model you must recognize

SQL Server database restore backup and recovery operation is based on three recovery models:

• Simple

• Full

• Bulk logged

It can introduce new features in the computer which you can further employ for proper functioning and transaction processes.

Simple model

Of all the models, simple recovery is the most common and popular option. It supports differential, full and file-level backup. However, transaction log backup is not supported. Moreover, it reuses the log space when the SQL Server process operation transpires. The unused part of the log file is eliminated and is now available for re-claim. Page restore and point-in-time do not get support, but the restoration of secondary files gets reinforced.

Now, there are a few reasons for you to select a simple information recovery model:

• Suitable for test and development of the database.

• Simple application or reporting database, where information loss is acceptable.

• The failure recovery is exclusive for differential and full backup.

• No requirement of administrative overhead.

It supports the following:

• Full backup

• File backup

• Differential backup

• Partial backup

• Copy-only backup

Since simple backup is easy to use and requires very little maintenance, you have every reason to employ them and use them to the best advantage. Remember that it is applicable for differential full and file backup but not transaction log backup.

Full model

The model takes care of all the transactions recorded in log records. Dissimilar from the simple recovery model, the log file does not undergo auto-truncation while checkpoint operation is on. The model unbreaks the log sequence and preserves the same for database restoration operation.

The model supports every restore operation, whether page restore, file restore, or point in time restore. Now the reasons that make this model popular among users are listed below:

• Support critical application

• Design for a high-availability solution

• Facilitate recovery of every data with minimal or zero data loss

• Restores individual pages

• Requires high-administration overhead

• Allows point-in-time restoration

• If the database gets designed for multiple filegroups, you may have to perform restoration mechanisms for writing, reading secondary filegroups. Hence, read-only file groups get support from this model.

Along with this, this recovery model supports every type of backup, which are listed below:

• Full backup

• Differential backup

• Partial backup

• File group backup

• Copy-only backup

• Log backup

Since the full recovery model is ideal for various transactions and helps backup every file, it is better for preserving the database and restoring operation.

Bulk logged model

Another special-purpose configuration option available that works similarly to the full recovery model is the bulk-logged model. These help in bulk operation while helping in minimal logging. The transaction log files use minimal logging techniques for bulk operation. However, it is hard to restore point-in-time information with this model. The reasons for selecting bulk-logged model are the following:

• Uses minimal logging method for preventing the growth of log files.

• If the database gets exposed to bulk operation, a bulk-logged model is the best option.

Moreover, it supports different types of backup, which are the follows:

• Full backup

• Partial backup

• Differential backup

• Transaction backup

• Copy-only backup

• File group backup

Now that you know so much about different recovery models, you may select the one that suits your requirement and fits your budget. Remember that every SQL Server issue is unique and requires a specific way of restoration. If you want to ensure proper maintenance of records and care of your log files, you may employ one of these recovery models. At times, it requires technical knowledge and expertise. Hence, using these models under the supervision of a professional will be the best option.

Transaction log internal

It would benefit if you dedicated your time to understanding the internals of the SQL Server log. If you are serious about your PC, you must comprehend the internals of SQL Server transactions.

• In the event of a transaction, the details of the operation are locked in the log file. • The log backup ensures data consistency and SQL fix by using write-ahead logging or WAL mechanisms. The transaction occurring on the database gets registered in the transaction log file. Following this, the information gets noted on a disk. The facility helps SQL Server roll forward or roll back every step in the recovery process.

• Enables restoration of point-in-time database.

• SQL Server writes sequentially to the transaction log file. It is a cynical process. The log file gets divided into various log blocks that get logically mapped using virtual log files or VLFs.

• The records in the log that are not required and get deemed as inactive, and that portion of log blocks may get truncated. Hence, the static segment of the log block remains overwritten by newer transactions. These portions or features of the log file are called VLF or virtual log files.

• If there is inactive VLF in the system, it may get truncated, but that depends on your recovery model.

• In the case of a basic recovery model, immediate truncation happens when there is a CHECKPOINT operation. The data pages get flushed into the disk after discovering the changes in the log file.

• A database consists of various log files, but you can have one. You may use one log file for writing necessary information because possessing more will not boost the writing speed. Instead, keeping more files may result in degradation of performance. If you do not size the files appropriately according to their nature and length, the mismatch might lead to a long duration of database recovery.

• In the case of an entrepreneurial, critical database, you may start full database backup and then go to the recurring transaction of log backup. When you back up your files, you can recover the same in times of emergency. It is a significant part of database restore operation and is a recent innovation in this field.

These are critical steps every PC user must keep in mind. Whether you go for a simple model or full model, or bulk-logged model, you must know the pros and cons of each. On the other hand, you may switch the recovery model from complete to bulk-logged, simple to a differential, or full to simple.