Questions tagged [database-internals]

For technical questions about the internal workings of the database engine.

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28
votes
1answer
5k views

Where are Statistics physically stored in SQL Server?

Where are the Statistics used by the Query Optimizer physically stored inside a SQL Server database file and the Buffer Pool? More specifically, is there a way to figure out the pages used by ...
3
votes
1answer
158 views

Directly acessing the NULL bitmap of a row in SQL Server

I was reading the question Checking a wide table for nulls and I'm wondering if it's possible to somehow directly access the NULL bitmap of a row to fast check if a row contains NULL values. Would ...
38
votes
4answers
19k views

Does the order of columns in a table's definition matter?

When defining a table, it's helpful to order the columns in logical groups and the groups themselves by purpose. The logical ordering of columns in a table conveys meaning to the developer and is an ...
2
votes
3answers
557 views

How is a join performed by a database engine?

How is a join between two tables actually performed by a database engine? I am sure that listing one tuple against all tuples of the other table cannot be the way to perform the join; it's just a ...
4
votes
1answer
1k views

What is a parse tree object?

I have looked into sys.syscachedobjects table. I found some records have an object type of parsetree. Can anyone tell me in detail what a parsetree is? Is this a data structure used by SQL Server, ...
13
votes
1answer
2k views

Slot Array and Total Page Size

I continue to read in many forums and on many blogs that a page is comprised as shown below: Page Size: 16 x 512B = 8192B Page Header: = 96B Maximum In_Row Row: = 8060B This leaves (...
0
votes
2answers
391 views

Which SQL Server system database is more important: master or resource? [closed]

Which SQL Server system database is more important: master or resource? If the resource database is damaged, can the database engine work? Can the system work with only the master database? If not, ...
4
votes
1answer
519 views

SQL Server Storage sql_variant

USE tempdb ; GO DROP TABLE tbl ; GO CREATE TABLE tbl ( i SQL_VARIANT NOT NULL ) ; GO INSERT INTO tbl (i) VALUES (1) ; GO SELECT i FROM tbl ; GO DBCC IND ('tempdb','tbl',-1) ; GO DBCC ...
1
vote
1answer
229 views

What is QP layer?

From blogs.innodb.com: InnoDB Memcached with Binlog Capability In our earlier Labs release, we presented a MySQL NoSQL solution through InnoDB Memcached Daemon Plugin (see earlier Calvin’s and my ...
1
vote
2answers
3k views

Is the mapping between PostgreSQL system tables and information_schema views documented?

If you connect pgadminIII to a PostgreSQL 9.x server, you'll find two catalogs exposed in the user interface: ANSI (information schema), and PostgreSQL (pg_catalog). I'm looking for documentation ...
5
votes
3answers
2k views

What could be the reason for disallowing a sub query in the values clause?

For example SQL> create table dates(d date); Table created. SQL> insert into dates select sysdate from dual; 1 row created. SQL> select * from dates; D --------- 28-MAY-11 SQL> ...

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