Data Directory 

This contains all of the user databases. Each database consists of a single directory within the Data directory. Within the database directories, there are table files that contain the actual table data. 

The format of a database table filename is: 

tablename_creation_id.dat 

or 

<table-name>_<creation-id>_<current-id>.dat 

where the <creation-id> is the unique table id number that was first assigned to the table when it was created and the <current-id> is the current unique table id number of the table. These numbers can also be found in the system database table systables. Tables are assigned an id number on creation and a new id number whenever the table is modified. 

 

System Tables Directory 

The system tables' .dat files are stored here, as well as the user-visible system tables, there are a few additional, internal, hidden tables. 

systemp.dat 

Temporary workspace, eg. for sorting queries. 

sysprocdql.dat 

Where the actual query plans of the system procedures go. derived from sysprocedures. 

sysundo.dat and sysxact.dat 

Storage of current transaction information. The nominal size of the transaction log can be specified. However, it will dynamically increase as required. This is a standard feature of all ACID database engines. For each server instance, there is one transaction log. These two files ensure all transactions during a crash are safely aborted. 

 

System Log Directory 

dbevents.log 

Human readable log of database events. It contains critical and informational errors about starting and stopping. 

sysredo.log and userredo.log 

The redo log is closely related to the transaction log. All modifications made to data pages are logged here. Where the transaction log contains the actual transaction being executed, the redo log records all of the physical row-level operations that have been performed. This is only used in crash recovery. For each database instance, there is one redo log. 

 

 

Related 

• ScimoreDB Architecture