VLDB Administration Strategies

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@murilocmirandahttp://www.sql.pt/[email protected]

AGENDA

AGENDA

1. What is a VLDB?2. Typical Troubles3. OS Config4. Instance Config5. DB Config6. Maintenance

VLDB??

VLDB??

There’s no official definition.

VLDB??


Typically occupying TB range.

VLDB??



Billions of rows.

VLDB??



Billions of rows.

Typically: OLAP or OLTP with large amount of users.

VLDB??

A very large database, or VLDB, is a database that contains an extremely high number of tuples (database rows), or occupies an extremely large physical filesystem storage space. The most common definition of VLDB is a database that occupies more than 1 terabyte or contains several billion rows, although naturally this definition changes over time.

Wikipedia…

SQL VS. VLDB

SQL VS. VLDB

Maximum database size

SQL VS. VLDB

Maximum database size

524,272 TB

SQL VS. VLDB

Maximum data file size16 TBMaximum log file size 2 TB

A limit of 32.767 files which can be distributed between 32.767 filegroups.

TYPICAL TROUBLES

TYPICAL TROUBLES

Maintenance

TYPICAL TROUBLES

Maintenance

Backups

TYPICAL TROUBLES

Maintenance

Backups

Indexes

TYPICAL TROUBLES

Maintenance

Backups

Indexes

Statistics

TYPICAL TROUBLES

Maintenance

Backups

Indexes

Statistics

Disaster Recovery

TYPICAL TROUBLES

Maintenance

Backups

Indexes

Statistics

Disaster Recovery

Performance

OS CONFIG

OS CONFIG

Perform Volume Maintenance

OS CONFIG

Turning on Instant Initialization to speed up data file growth and restores.

OS CONFIG

Storage Layout

OS CONFIG

Plan an efficient storage layout.

OS CONFIG


Normally, the more spread, the more effective.

OS CONFIG


Normally, the more spread, the more effective.

Suggestion:

SQL BINSQL DATASQL IDXSQL LOGS SQL TMP

OS CONFIG

Mountpoints

OS CONFIG

Mountpoints could be a good strategy.

OS CONFIG

Mountpoints could be a good strategy.

Mountpoints are persistent directories that point to disk volumes.

OS CONFIG

Pros:

• Scalable.• Save drive letters (limited to 26).• Easy to add.• No need to restart SQL Server.

OS CONFIG

Cons:

• Looks like a simple folder.• Need a different approach to monitor.

OS CONFIG

So, if you don’t know the server….

OS CONFIG

Partition Alignment

OS CONFIG

Setting the partition offset properly can improve up to 30% the performance.

OS CONFIG

Setting the partition offset properly can improve up to 30% the performance.Partition alignment increases

throughput (bytes/sec) and reduce disk queues.

OS CONFIG

Setting the partition offset properly can improve up to 30% the performance.Partition alignment increases

throughput (bytes/sec) and reduce disk queues.

A partition that is track misaligned will occasionally cause 2 I/O operations instead of one.

OS CONFIG

Unless performed at the time of partition creation, the default alignment offset (31,5 Kb) will result in unaligned partitions on versions of Windows up to and including Windows Server 2003.

OS CONFIG

This offset is associated with hidden sectors,which basically store partition information.

OS CONFIG

This offset is associated with hidden sectors,which basically store partition information.Considering that:

- Each disk sector has 512 bytes.- Win. 2003 has 63 hidden sectors.

OS CONFIG

This offset is associated with hidden sectors,which basically store partition information.Considering that:

- Each disk sector has 512 bytes.- Win. 2003 has 63 hidden sectors.

512 * 63 = 31,5 Kb

OS CONFIG

Example:

Stripe Unit Size: 64Kb*Allocation Unit Size: 64Kb

* Defined by storage team.

Optimal values

OS CONFIG

Example:

Stripe Unit Size: 64Kb*Allocation Unit Size: 64Kb

* Defined by storage team.

Optimal values

Stripe Size

Data (Alloc. Unit Size)

OS CONFIG

Optimal solution:

Stripe Size

Data (Alloc. Unit Size)

OS CONFIG

Best Practice:

- Set an offset of 1024 Kb.- This value works for mostly disks out there.

- Allocation Unit Size = Stripe Unit Size.

The rule: Offset / Allocation unit = INTEGER Eg: 1024/64=16

Some I/O subsystem vendors intercepting what Windows is trying to do and are still creating partitions with the incorrect offset – Even for Windows 2008+.

WARNIG

ALWAYS check!

OS CONFIG

Anti-Virus in servers… is really a need?

OS CONFIG

• Cost money to license.• Maintenance costs.• Can cause problems in Prod.• Can’t protect to zero-day exploits.

OS CONFIG

What can we do instead?

OS CONFIG

• Keep the servers patched.• Configure the firewall properly.• Restrict server’s access.• You can install AV… in workstations!

OS CONFIG

What’s the big problem for SQL Server?

OS CONFIG

• One more app fighting for resources.• SQL Server files can be locked.

OS CONFIG

How can AV and SQL Server live together?

OS CONFIG

Add exceptions!

OS CONFIG

Basically the AV should ignore:

• SQL Server data and log files (.mdf, .ndf and .ldf).• Backup files (.bak and .trn).• Full-text Catalog files.• Trace files (.trc).• ERRORLOG files.• SQL Server binaries folder.• Filestream folder.

More on: http://support.microsoft.com/kb/309422

INSTANCE CONFIG

INSTANCE CONFIG

Memory

INSTANCE CONFIG

Memory

This is a very open subject.

INSTANCE CONFIG

Memory


There are lots of discussions about that…

INSTANCE CONFIG

Memory



There’s no perfect formula, because the correct awnser is….

INSTANCE CONFIG

Memory



There’s no perfect formula, because the correct answer is….

… it depends !!

INSTANCE CONFIG

Memory

Baseline: 1 GB for the OS

Up to 16 GB available• 1 GB for each 4 GB

More than 16 GB• 1 GB for every 8 GB

An efficient general rule…

INSTANCE CONFIG

Memory

This is for 64 bit servers…

For 32 bit, here is a good article to follow:http://www.eraofdata.com/understanding-and-configuring-sql-servers-memory-settings/

INSTANCE CONFIG

TempDB

INSTANCE CONFIG

TempDB

Two common behaviors:

INSTANCE CONFIG

TempDB

Two common behaviors:• Ignore.• Overvalue.

INSTANCE CONFIG

TempDB

As per Brent Ozar:

“TempDb is the SQL’s public toilet”

INSTANCE CONFIG

TempDB

And this is true!

INSTANCE CONFIG

TempDB

INSTANCE CONFIG

TempDB

There’s a myth:• tempdb should always have one data file per processor core.

INSTANCE CONFIG

TempDB


Again….

INSTANCE CONFIG

TempDB


Again…. It depends!

INSTANCE CONFIG

TempDB

Execute large operations, like a sort or store a huge temporary table,may be slowed down because of the round-robin operation.

The more files, the more costly.

INSTANCE CONFIG

TempDB

Common wait types on TempDB:

• PAGELATCH_*: Contention for In-memory allocation bitmaps. • PAGEIOLATCH_*: Contention at the I/O subsystem level.

INSTANCE CONFIG

TempDB

How many tempdb data files should we have?

INSTANCE CONFIG

TempDB

How many tempdb data files should we have?A recommended approach is:• Up to 8 cores:

Number of files = Number of cores.

• More than 8 cores: 1. Add 8 files.2. Monitor PAGELATCH_*.3. Add 4 more files at a time, if necessary.

INSTANCE CONFIG

TempDB

Other TempDB best practices:• Isolate the TempDB in a different storage system.• Depending of the load, you might need to separate

LDF and M(N)DF. • Use a fast drive (SSD :).• Set an initial size, equally to all the files.

• Set the auto-growth accordingly.• If you have a heavy operation using constantly the

TempDB, consider create a staging table into your own database.

INSTANCE CONFIG

TempDB

From SQL Server 2012, local disk TempDB in SQL Server cluster.

INSTANCE CONFIG

TempDB

From SQL Server 2012, local disk TempDB in SQL Server cluster.

• More flexibility.• Use PCIe bus instead of HBA, and have more

throughput.• Data and Log are in SAN, TempDB locally: Avoid

congestion or contention on a shared storage network or array.

DB CONFIG

DB CONFIG

• Don’t rely on auto-grow.• You can manage file growth and control the

free disk space and avoids performance problems.

DB CONFIG



• Have page checksums turned on.• To detect damaged pages.

DB CONFIG



• Have page checksums turned on.• To detect damaged pages.

• Make sure auto-stats update is turned on.• For OLTP consider turning auto-stats update

off only for heavily updated tables, and schedule a job that periodically updates the statistics for those tables.

DB CONFIG

DB CONFIG

• Make sure you’re managing the transaction log correctly:• Full recovery requires log backups.• No advantage in have multiple log files.• Control the file growth or this could

cause VLF fragmentation.• Performance issues.• Slow backup time.

• Don’t set the log file growth size to a multiple of 4 in older SQL Server versions.• http://connect.microsoft.com/SQLServer/feedback/details/481594/log-growth-

not-working-properly-with-specific-growth-sizes-vlfs-also-not-created-appropriately

MAINTENACE

MAINTENANCE

Few questions…

MAINTENANCE

Is data-loss acceptable?

What about the recovery time?

How to meet your SLAs dealing with a TB database?

Are you able to UPDATE STATS, do INDEX MAINTENANCE and run a INTEGRITY CHECK in time and WITHOUT PROBLEMS?

MAINTENANCE

DISASTER RECOVERY

MAINTENANCE

First of all, think in a Disaster Recovery plan!

SQL Server is not Oracle, we have “free” included options:• Log Shipping (HA and DR)• Database Mirroring (HA and DR)

• DB Snapshot advantage

• Replication (HA, DR and LB)• AlwaysOn (HA, DR and LB)

• We can still be safe with a storage level replication.

MAINTENANCE

PartitionCompressClean

MAINTENANCE

Partition, Compress and Clean

Using the partitioning feature you can devise the maintenance.

MAINTENANCE



• You can use the DBCC CHECKFILEGROUP command.• DBCC CHECKFILEGROUP and DBCC CHECKDB are. The main

difference is that DBCC CHECKFILEGROUP is limited to the single specified filegroup and required tables.

MAINTENANCE



• Devising a filegroup architecture allows piecemeal restores with low TTR • Online piecemeal restore:

• After the PRIMARY FG restore the DB can be online.• The tables will come available while each FG is restored.

• Design the database accordingly:• Keep the necessary into the PRIMARY FG.

• Configuration tables, indispensable data, etc…• Think in the consistency: keep related tables in the same

FG.

MAINTENANCE


Compress backups Vs. Compress Data

• Backup compression:• More CPU usage to backup/restore (avg ~20%).• Less time to backup/restore (avg ~40%).• Good compression ratio.

• SELECT backup_size/compressed_backup_size FROM msdb..backupset;

• A backup set will not be able to contain both compressed and uncompressed backups.

• No advantage with TDE enabled.

MAINTENANCE


Compress backups Vs. Compress Data

• Data compression (ROW and PAGE):• TDE and Data Compression play together!• Backup and Data Compression can coexist!

MAINTENANCE


Purge and Archive the data

• Purging data:• If data is needed no more…• Save storage.• Faster backups.• Improves the performance.

MAINTENANCE


Purge and Archive the data

• Archiving data:• If data is still needed…• Isolate in a different FG.• Set as Read-Only: Avoids locking.

• For faster scans: 100% fill factor.• Update statistics with FULLSCAN.

• You can adapt the backup strategy.• You can adapt the backup strategy using Partial

Backups.• This allows you to exclude read-only filegroups.

MAINTENANCE

More about DBCC CHECKDB• CHECKDB takes time and uses resources.

• Run a DBCC CHECKDB using the WITH PHYSICAL_ONLY option.• Limits the checking to the integrity of the physical structure of

the page and record headers and the allocation consistency of the database.

• Faster, but a full CHECKDB is required periodically.

MAINTENANCE

More about DBCC CHECKDB• We can divide up the consistency checking over several

days, Paul Randal’s prescription is:• Divide tables in two buckets (bigger ones and the rest)

• On Sunday:• Run a DBCC CHECKALLOC• Run a DBCC CHECKCATALOG• Run a DBCC CHECKTABLE on each table in the first bucket

• On Monday, Tuesday, Wednesday:• Run a DBCC CHECKTABLE on each table in the 2nd, 3rd, 4th

buckets, respectively• On Thursday:

• Run a DBCC CHECKALLOC• Run a DBCC CHECKTABLE on each table in the 5th bucket

• On Friday and Saturday:• Run a DBCC CHECKTABLE on each table in the 6th and 7th

buckets, respectively

More on: http://www.sqlskills.com/blogs/paul/checkdb-from-every-angle-consistency-checking-options-for-a-vldb/

MAINTENANCE

More about BACKUPS• Besides doing PARTIAL BACKUPS we have more options…• A MULTISTREAM BACKUP is an option to run faster:

DB

File 1

File 2

File 3

E:

G:

F:

MAINTENANCE

More about BACKUPS• To make sure it will be well stored, we can use a MIRROR.

DB

File 1

File 2

File 3

E:

G:

F:

File 1

File 2

File 3

MAINTENANCE

More about BACKUPS• If storing to the network:

• Use a separate network card to avoid network congestion.

• Don’t forget about T-LOG backups!• Create a good backup strategy.

• Verify the backups periodically.

MAINTENANCE

INDEXES MAINTENANCE• Only rebuild/defrag indexes that are really fragmented

(avoid unnecessary work in short maintenance windows)

• If you defrag instead of rebuild, make sure you manually update stats.

• Be wary of doing large index maintenance jobs if you use log shipping or DBM• They contribute to large log backups• Index rebuilds are always full-logged when DBM is

present

QUESTIONS?

OBRIGADO!@murilocmirandahttp://www.sql.pt/[email protected]

Technology

VLDB Administration Strategies