Text From The Slides Of The Miami Technical Tutorial + Text From The Slides Of The Miami Technical Tutorial + Text From The Slides Of The Miami Technical Tutorial On DBMS-11 Presented By Ann Harrison Of DEC + On DBMS-11 Presented By Ann Harrison Of DEC + On DBMS-11 Presented By Ann Harrison Of DEC Two Topics: New Features Of DBMS-11 Ver. 1.8 Database Control System (DBCS) Communication *** New Features *** o Multiple Databases Per Computer System o Reduced Journalling Requirements o Database Logger Enhancements o New DBO Commands o Variable Length And Page Size For Data Dictionaries -------------------------------------------------------------------- 1. Multiple Databases Per Computer System User tasks map to a database by default UIC o One task can access only one database o Tasks need not be recompiled or taskbuilt to access another database. Each active database has its Database Manager. o Minimum duplication of active tasks. o Minimum contention for data buffers. Redirection table associates a database device and UIC with user defualt UIC. Redirection table is maintained with DBO. Redirection table entries can include wild card specificatons for database and user. DBX searches redirection table entries from first to last accepting first match. Number of simultaneously active databases is an installation option. o Five is the maximum supported. o Each DBM task requires approximately 70KB of memory. Number of databases on system is not limited. 2. Journalling Defined in the Schema Allowed or disallowed in the DMCL Altered at runtime by DBO commands to: o Disallow journalling o Disregard retrieval only run units o Disregard before images o Disregard after images o Disallow autorecovery Maintains a single journal file although state changes Changes state only at a quiescent point Writes state into journal records Allows recovery programs to report absence of required page images. 3. Database Logger Enhancements Error log is written to console terminal More information is written to a log file [1,4]DBMS11.LOG. Expanded log can be written to log file [1,4]DBMS11DBG.LOG. Trace log can be written to file [1,4]DBMS11TRC.LOG. Log files are assigned to devices when DBL is taskbuilt 4. New DBO Commands START/STOP/EXIT/ABORT Users can not sign on to a stopped database. Any one database or all databases may be stopped. Some system operations require that the database be stopped (ie. changing journalling). INITIALIZE replaces DBINIT o Operator can specify create or delete files BACKUP/RESTORE replace DBDUMP/DBRESTORE o Operator can specify error limit JOURNALLING o SET or SHOW journalling options Redirection Tables o DEFINE or DELETE redirection table entries 5. Variable length and page size for Data Dictionaries. Since a Data Dictionary is required to use Datatrieve, DBQ, DML preprocessors, etc. and since the page size for user data areas must be the same as the dictionary page size, and since not all databases require 2000 blocks of dictionary, V1.8 will allow users to set dictionary page size and page range. ------------------------------------------------------------------------- DATABASE CONTROL SYSTEM COMMUNICATION What is DBCS ? The formal names are: 1. INTERFACE ROUTINES (DBMS01) 2. DBMS11 (SLV) 3. DBMDBX (DBX) 4. DBM.00 - DBM.04 (DBM) 5. DBMDBL (DBL) 6. Inter-Task Connections 1.0 Interface Routines Object modules linked from SYSLIB into user tasks Slightly different set for COBOL DML than for FORTRAN Called generically DBMS01 Translate DML calls to DBCS requests 2.0 DBMS11 Generally a task slaved to the user task except for some 11M Plus systems. Called familiarly "slave" spelled SLV. Introduces a user task to DBCS 3.0 DBMDBX The database executive, called DBX During user sign-on: o Maps user to database o Checks that database is started o Invokes a new DBM if required If a user aborts, DBX notifies DBM There is only one DBX on any system 4.0 DBMDBL The database logger, called DBL Reads the error message file Writes log messages to the console Writes log files: DBMS11,DBMS11DBG, DBMS11TRC 5.0 DBM.00 -> DBM.04 The database managers, called DBM Handle database functions like: o FIND, GET, Journalling, Concurrency control, etc. One per active database 6.0 Inter-Task Connections To recognize system and user failuresm the DBCS tasks recieve AST notification of the exit of other tasks. DBX connects to SLV, each DBM, DBL, and to each user. DBM tasks connect to DBL and DBX. DBL connects to DBX and each DBM. User tasks and SLV do not recieve notification of DBCS task exits, but time out in case of system failure.