What is the difference between partition and page in SQL Server? Is these are available by default or we need to create explicitly?
Page is the most basic element of storage in SQL Server.
In SQL Server, the page size is 8 KB. This means SQL Server databases
have 128 pages per megabyte. Each page begins with a 96-byte header
that is used to store system information about the page. This
information includes the page number, page type, the amount of free
space on the page, and the allocation unit ID of the object that owns
the page.
Partition:- Partitioning allows a table, index, or index-organized table to be subdivided into smaller pieces, where each piece of such a database object is called a partition. Each partition has its own name, and may optionally have its own storage characteristics. The data of partitioned tables and indexes is divided into units that can be spread across more than one filegroup in a database. The data is partitioned horizontally, so that groups of rows are mapped into individual partitions.
SQL Server 2012 supports up to 15,000 partitions by default. In
earlier versions, the number of partitions was limited to 1,000 by
default. On x86-based systems, creating a table or index with more
than 1000 partitions is possible, but is not supported.
Related
I want to enable a system versioning for some table in SQL Server. As I understand, the new history table would be created with the same values as current tables, plus I create two new datetime2 columns. Am I right that just enabling system versioning at least doubles the storage space?
As I understand, the new history table would be created with the
same values as current tables, plus I create two new datetime2
columns. Am I right that just enabling system versioning at least
doubles the storage space?
No.
The history table contains non current versions of rows so it is empty until you start deleting or updating rows in the main table.
So storage space will increase by whatever factor the addition of the two new datetime2 columns makes to row width and then depend on your rate of updates and deletes that invalidate existing row versions and cause rows to be stored in the history table.
NB: By default, the history table is PAGE compressed. You might also create it a clustered columnstore to achieve potentially greater levels of compression.
Need to exceed the 8k record limit in SQL Server 2008 when using wide columns/sparse tables.
Long story new client old system using survey system, pivoting data so all answers are a column
I have 1500 columns and now I am getting
Cannot create a row that has sparse data of size 9652 which is greater than the allowable maximum sparse data size of 8019.
I need to exceed the 8k record limit if possible
Not possible, because SQL Server stores rows on 8K pages. The only way to do so would be to store some of the data off-row (e.g. using MAX or other LOB types for some of your columns). To your application, this will still look like it's on the same row, even though logically it is on a complete different area of disk.
If your sparse column set alone exceeds the limit, sorry, you'll need to look at a different way to store the data (either not pivoted, EAV, or simply use two tables joined by a key, each containing half of the column set). For the latter you can make this relatively transparent to users by using views and/or enforcing all data access / DML through stored procedures that understand the division.
For example, a website offers the ability to create mobile surveys. Each survey ID is a FK in the survey response table, which contains ALL of the survey responses.
What is the size limitation of this table in a SQL Server 2008 db, if the table contains, say 20 varchar(255) fields including the bigint PK & FK?
I realize this would depend on the file size limitation as well, but I would like some more of an educated answer rather than my guess on this.
In terms of searchability, some fields that contain geo-related details such as the survey ID, city, state, and two commends fields would have to be searchable, and thus indexed ... index only these fields?
Also, aged responses would expire after a given amount of time - thus deleted from the table. Does the table, at this point being very large, need to be re-indexed/cleaned up, after the deletions (which would be an automated process)?
Thanks.
Maximum Capacity Specifications for SQL Server
Bytes per row: 8,060
Rows per table: Limited by available storage
Note
SQL Server supports row-overflow storage which enables variable length
columns to be pushed off-row. Only a 24-byte root is stored in the
main record for variable length columns pushed out of row; because of
this, the effective row limit is higher than in previous releases of
SQL Server. For more information, see the "Row-Overflow Data Exceeding
8 KB" topic in SQL Server Books Online
You mention 'table size' -- does this mean number of rows?
Maximum Capacity Specifications for SQL Server
Rows per table : Limited by available storage
As per this Reference, the max size of a table is limited by the available storage.
It sounds like you are going to have a high traffic and high content table. You should consider performance and storage enhancements like Table Partitioning. Also, because this table will be the victim of often INSERTS/UPDATES/DELETES, carefully plan out your indexing, as indexes add overhead for DML statements on the table.
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How is data stored in SQL server?
This Wikipedia article describes it rather well.
Here is a subset of it, relating to Data Storage:
Data storage The main unit of
data storage is a database, which is a
collection of tables with typed
columns. SQL Server supports different
data types, including primary types
such as Integer, Float, Decimal, Char
(including character strings), Varchar
(variable length character strings),
binary (for unstructured blobs of
data), Text (for textual data) among
others. It also allows user-defined
composite types (UDTs) to be defined
and used. SQL Server also makes server
statistics available as virtual tables
and views (called Dynamic Management
Views or DMVs). A database can also
contain other objects including views,
stored procedures, indexes and
constraints, in addition to tables,
along with a transaction log. A SQL
Server database can contain a maximum
of 231 objects, and can span multiple
OS-level files with a maximum file
size of 220 TB. The data in the
database are stored in primary data
files with an extension .mdf.
Secondary data files, identified with
an .ndf extension, are used to store
optional metadata. Log files are
identified with the .ldf
extension.
Storage space allocated to a database
is divided into sequentially numbered
pages, each 8 KB in size. A page is
the basic unit of I/O for SQL Server
operations. A page is marked with a
96-byte header which stores metadata
about the page including the page
number, page type, free space on the
page and the ID of the object that
owns it. Page type defines the data
contained in the page - data stored in
the database, index, allocation map
which holds information about how
pages are allocated to tables and
indexes, change map which holds
information about the changes made to
other pages since last backup or
logging, or contain large data types
such as image or text. While page is
the basic unit of an I/O operation,
space is actually managed in terms of
an extent which consists of 8 pages. A
database object can either span all 8
pages in an extent ("uniform extent")
or share an extent with up to 7 more
objects ("mixed extent"). A row in a
database table cannot span more than
one page, so is limited to 8 KB in
size. However, if the data exceeds 8
KB and the row contains Varchar or
Varbinary data, the data in those
columns are moved to a new page (or
possibly a sequence of pages, called
an Allocation unit) and replaced with
a pointer to the data.
For physical storage of a table, its
rows are divided into a series of
partitions (numbered 1 to n). The
partition size is user defined; by
default all rows are in a single
partition. A table is split into
multiple partitions in order to spread
a database over a cluster. Rows in
each partition are stored in either
B-tree or heap structure. If the table
has an associated index to allow fast
retrieval of rows, the rows are stored
in-order according to their index
values, with a B-tree providing the
index. The data is in the leaf node of
the leaves, and other nodes storing
the index values for the leaf data
reachable from the respective nodes.
If the index is non-clustered, the
rows are not sorted according to the
index keys. An indexed view has the
same storage structure as an indexed
table. A table without an index is
stored in an unordered heap structure.
Both heaps and B-trees can span
multiple allocation units.
SQL Server data is stored in data files that, by default, have an .MDF extension. The log (.LDF) files are sequential files used by SQL Server to log transactions executed against the SQL Server instance (more on instances in a moment). The log files (.LDF files) are truncated automatically when using the SIMPLE recovery model, but not when using BULK LOGGED or FULL recovery.
Instances allow for more than one installation of SQL Server on a single machine. If the instance is nameless, it is the default instance. Named instances are possible as well. For eg:
MACHINENAME <-- the default instance is just the machine name
MACHINENAME\Test <-- this is the "Test" instance on this machine
You can use tools like SQL Server Management Studio (as of SQL Server 2005) or Enterprise Manager (SQL Server 2000 and before) to interact with the instance & the databases under the instance.
All instances (as of SQL Server 2005) will have a hidden resource database, as well as a master, model, msdb, and temp database. These databases are "system" databases.
Not sure what else you're looking for. Hope that helps.
EDIT:
Oh yeah, physically, data in the "data files" (.MDF files, by default) is structured in what are known as "pages" in SQL Server. Data in the log files (.LDF files) is stored sequentially. In the enterprise, the data and log files are sometimes split on different physical hard drives for better disk I/O. Or hardware RAID is used for this purpose.
EDIT2:
Forgot to mention file groups. Using file groups, you can design your logical database schema such that elements of that schema are physically separated, typically to disburse the physical database across different hard drives. For example, you could have a data file group, an indexes file group, and an images file group (for binary images).
I recommend the book 'Microsoft SQL Server 2008 Internals' -- in fact anything by Kalen Delaney on internals is good, IMO.
SQL Server is a Relational Database Management System:
A Relational database management
system (RDBMS) is a database
management system (DBMS) that is based
on the relational model as introduced
by E. F. Codd. Most popular commercial
and open source databases currently in
use are based on the relational model.
A short definition of an RDBMS may be
a DBMS in which data is stored in the
form of tables and the relationship
among the data is also stored in the
form of tables.
You can take this just about as deep as you want to go, but for SQL Server 2008 Files and Filegroups Architecture - MSDN is a good overview of basic database architecture.
The MSDN site will be a valuable resource if you need even more detailed specifics on how SQL Server 2008 stores data.
What is RDBMS?
RDBMS stands for Relational Database Management System. RDBMS data is structured in database tables, fields and records. Each RDBMS table consists of database table rows. Each database table row consists of one or more database table fields.
RDBMS store the data into collection of tables, which might be related by common fields (database table columns). RDBMS also provide relational operators to manipulate the data stored into the database tables. Most RDBMS use SQL as database query language.
Edgar Codd introduced the relational database model. Many modern DBMS do not conform to the Codd’s definition of a RDBMS, but nonetheless they are still considered to be RDBMS.
The most popular RDBMS are MS SQL Server, DB2, Oracle and MySQL.
Source
Background
I have a massive db for a SharePoint site collection. It is 130GB and growing at 10gb per month. 100GB of the 130GB is in one site collection. 30GB is the version table. There is only one site collection - this is by design.
Question
Am I able to partition a database (SharePoint) using SQL 2005s data partitioning features (creating multiple data files)?
Is it possible to partition a database that is already created?
Has anyone partitioned a SharePoint DB? Will I encounter any issues?
You would have to create a partition set and rebuild the table on that partition set. SQL2005 can only partition on a single column, so you would have to have a column in the DB that
Behaves fairly predictably so you don't get a large skew in the amount of data in each partition
IIRC the column has to be a numeric or datetime value
In practice it's easiest if it's monotonically increasing - you can create a series of partitions (automatically or manually) and the system will fill them up as it gets to the range definitions.
A date (perhaps the date the document was entered) would be ideal. However, you may or may not have a useful column on the large table. M.S. tech support would be the best source of advice for this.
The partitioning should be transparent to the application (again, you need a column with appropriate behaviour to use as a partition key).
Unless you are lucky enough to have a partition key column that is also used as a search predicate in the most common queries you may not get much query performance benefit from the partitioning. An example of a column that works well is a date column on a data warehouse. However, your Sharepoint application may not make extensive use of this sort fo query.
Mauro,
Is there no way you can segment the data on a Sharepoint level?
ie you may have multiple "sites" using a single (SQL) content database.
You could migrate site data to a new content database, which will allow you to reduce the data in that large content site and then shrink the datafiles.
it will also assist you in managing your obvious continued growth.
James.