Operating in DSE

The GT.M Database Structure Editor, DSE, is primarily a tool for authorized GT.M consultants to examine and, under unusual circumstances, repair GT.M Database Structure (GDS) databases. With DSE, it is possible to see and change most of the attributes of a GT.M database.

DSE gives all possible control over a database and therefore, it may cause irreparable damage when used without knowing the consequences. Therefore, you unless you have extensive experience, you should always get guidance from FIS or an equivalently knowledgeable support resource before running any DSE command that changes any attribute of any production database or other database you value. Use utilities and commands like %PEEKBYNAME, MUPIP DUMPFHEAD, GVSTATS, %YGBLSTAT, etc. Only use DSE for collecting database metrics and monitoring status in an unusual situation where safer tools are unavailable.

GT.M installation procedure places the DSE utility program in a directory specified by the environment variable gtm_dist.

Invoke DSE using the "dse" command at the shell prompt. If this does not work, consult your system manager to investigate setup and file access issues.

Example:

$gtm_dist/dse
File/usr/name/mumps.dat
Region  DEFAULT
DSE>

DSE displays the DSE> prompt.

You may also specify a command when entering DSE.

By default, DSE starts with the region that stands first in the list of regions arranged in alphabetical order. In the above example, the first region is DEFAULT.

You may also specify a command when entering DSE.

Example:

$gtm_dist/dse dump -fileheader

This command displays the fileheader of the region that stands first in the list of regions arranged in alphabetical order and then returns to the shell prompt. To look at other regions, at the DSE prompt you must first issue a FIND -REGION=<desired-region> command.

As previously mentioned, DSE provides control over most of the attributes of your database. With DSE, it is possible to examine them and,with a few exceptions, change them.

All DSE commands are divided into two categories-Change commands and Inquiry commands. Change commands allow you to modify the attribute of your database, in most cases without any warning or error. As the low level tool of last resort, Change commands allow you to take certain actions that can cause extensive damage when undertaken without an extensive understanding of the underlying data structures on disk and in memory and with an imperfect understanding of the commands issued. Do not use the Change commands unless you know exactly what you are doing and have taken steps to protect yourself against mistakes, both inadvertent and resulting from an incomplete understanding of the commands you issue. Change commands are not required for normal operation, and are usually only used under the direction of FIS support to recover from the unanticipated consequences of failures not adequately planned for (for example, you should configure GT.M applications such that you never need a Change command to recover from a system crash). Use Inquiry commands sparingly and only when there is no alternate available.

The list of Change commands is as follows:

AD[D]
AL[L]
B[UFFER _FLUSH]
CH[ANGE]
CR[ITICAL]
REM[OVE]
RES[TORE]
SH[IFT]
W[CINIT]
OV[ERWRITE]
M[APS] -BU[SY] -F[REE] -M[ASTER] -R[ESTORE_ALL]

The list of Inquiry commands is as follows:

CL[OSE]
D[UMP]
EV[ALUATE]
EX[IT]
F[IND]
H[ELP]
I[NTEGRIT]
M[APS] -BL[OCK]
OP[EN]
P[AGE]
RA[NGE]
SA[VE]
SP[AWN]

Although DSE can operate concurrently with other processes that access the same database file, FIS strongly recommends using DSE in standalone mode when using Change commands. Some DSE operations can adversely impact the database when they occur during active use of the database. Other DSE operations may be difficult to perform in a logically sound fashion because a DSE operator works on a block at a time, while normal database operations update all related blocks almost simultaneously.

[Caution]Caution

When DSE attaches to a database with a version that does not match the DSE version, DSE issues an informational message and continues. At this point, you should exit DSE and find the version of DSE that matches the database. You should continue after this warning if and only if you are certain that the DSE is indeed from the GT.M version that has the database open (and hence the error results from a damaged database file header or shared memory that you intend to repair, following instructions from FIS).

Use the DSE EXIT, or QUIT command to leave DSE.

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