DCMT DISPLAY BUFFER Command

DCMT DISPLAY BUFFER displays information about a specified database or journal buffer, including its associated files and areas.
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DCMT DISPLAY 
BUFFER
 displays information about a specified database or journal buffer, including its associated files and areas.
DCMT DISPLAY 
BUFFERS
 displays information about all database and journal buffers defined to the runtime system.
This article describes the following information:
 
 
Syntax
►►─── DCMT ─┬───────────────────┬─────────────────────────────────────────────► └─
broadcast-parms
─┘ ►─── Display ──────┬─ Buffer ─┬─
buffer-name
─┬────────┬─┬─┬─────────────────►◄ │ │ ├─ ARea ─┤ │ │ │ │ ├─ File ─┤ │ │ │ │ ├─ LOC ──┤ │ │ │ │ └─ ALl ──┘ │ │ │ └─
buffer-star-name
───────┘ │ └─ Buffers ─────────────────────────────┘
Parameters
  •  
    broadcast-parms
    Indicates to execute the DCMT command on all or a list of data sharing group members.
     For more information about broadcasting and 
    broadcast-parms
     syntax, see the section How to Broadcast System Tasks.
  •  
    Buffer
    Displays information about a specified database or journal buffer.
  •  
     
    buffer-name
     
    The name of a buffer.
  •  
    ARea
    Displays information about the specified buffer and its associated areas.
  •  
    File
    Displays information about the specified buffer and its associated files. For files using shared cache, displays the shared cache status (Yes, No, or Available) and the name of the cache for the named file or files to which the buffer is mapped.
  •  
    LOC
    Displays the address of the buffer control block.
  •  
    ALl
    Displays information about the specified buffer and its associated files and areas.
  •  
     
    buffer-star-name
     
    Displays information about all buffers whose names begin with the same specified alphanumeric characters.
    Buffer-star-name
     specifies any alphanumeric description that ends with an asterisk (*) to denote wild card characters.
    In this example, CA IDMS displays information about all buffers that begin with the letters JKD:
    dcmt d b jkd*
  •  
    Buffers
    Displays information about all buffers.
Usage
 
Display for Each Buffer
 
DCMT DISPLAY BUFFERS displays the following information for each buffer:
 
Field
 
 
Value
 
Data Buffer
Name of the buffer
Size
Buffer size, in bytes
In-Use
Current number of pages assigned to the buffer
Max
Maximum number of pages that can be assigned to the buffer
Getstg
An indicator if the buffer is allocated from operating system storage or from a DC/UCF storage pool
Prfetch=Min
The minimum number of pages that must be in the buffer before prefetch is used for every read request
Prefetch
If prefetch processing is allowed or disabled for the buffer
Journal Buffer
Name of the journal buffer
Size
Buffer size, in bytes
# In-Use
Current number of journal blocks in use
Waits
Number of times a task had to wait for a journal buffer to become available (all journal buffers were involved in an I/O)
DB
Number of writes of journal blocks due to the system writing a database buffer to the database
Ckpt
Number of writes of journal blocks due to a COMT, ENDJ, or ABRT checkpoint record
# of Recoveries
Number of times the system had to rollback changes
I/O's
Number of journal blocks used in recovery that had to be read from the journal file (I/O required)
in Buffer
Number of journal blocks used in recovery that were found in the journal buffer (no I/O required)
Waits on Prior IO
Number of times tasks had to wait for previously issued journal writes to complete
Forced IO: Deadlock
Number of times the system was forced to write the active journal buffer due to a deadlock preventing other tasks from filling the active journal buffer (which would normally cause the active journal buffer to be written)
Split
Number of times I/O was forced to avoid a small split journal record
 
Display for the Specified Buffer
 
In addition to the information listed above, DCMT DISPLAY BUFFER 
buffer-name
 displays the relevant portions of the following information for the specified buffer:
  • Synonym Table
 
Field
 
 
Value
 
User-defined
The user defined maximum number of full-word entries in the synonym table.
System-Calculated
The system calculated maximum number of full-word entries in the synonym table. This is calculated by multiplying the maximum number of pages in the buffer by two and then rounding up to the nearest power of two.
Total-space Used
The number of bytes actually used by the synonym table.
  • Allocation
 
Field
 
 
Value
 
Initial
The number of pages initially allocated for the buffer.
Addit'l
The number of pages to be reserved for the buffer each time more pages need to be reserved.
Num-alloc
The number of times more pages have been added to the buffer.
Size-Init
The number of bytes used for the initial allocation of pages for the buffer.
Size-Add'l
The number of additional bytes allocated to the buffer.
Tot-space
The total number of bytes allocated to the buffer.
  • Storage
 
Field
 
 
Value
 
Stg-pools
The number of bytes allocated to the buffer from storage pools.
Getmain'd
The number of bytes allocated to the buffer from the operating system.
Above-16mb
The number of bytes allocated to the buffer from above the 16-megabyte line.
Below-16mb
The number of bytes allocated to the buffer from below the 16-megabyte line.
Total
The total number of bytes allocated to the buffer.
 
Area and File Information
 
If you specify AREA, FILE, or ALL, you receive information on the associated area(s), file(s), or both. See the description of DCMT DISPLAY AREA and/or DCMT DISPLAY FILE for further documentation.
Examples
 
DCMT DISPLAY BUFFER
 
D BUFFER --- Data Buffer -- Size In-use Max Getstg Prfetch-Min Prefetch DEFAULT_BUFFER 4276 30 60 OPSYS 500 Not-Allowd LOG_BUFFER 4276 Not Open 0 OPSYS DBCR_ACCT_BUFFER 2932 490 1470 OPSYS 500 Not-Allowd DBCR_BRCH_BUFFER 4000 200 1000 OPSYS 500 Not-Allowd - Journal Buffer - Size # In-Use Waits DB Ckpt JNL_BUFFER 2004 5 0 17 17 # of Recoveries I/O's in Buffer 0 0 0 Waits on Prior IO Forced IO: Deadlock Split 0 0 7
 
DCMT DISPLAY BUFFER buffer-name
 
D BUFFER DBCR_ACCT_BUFFER --- Data Buffer -- Size In-use Max Getstg Prfetch-Min Prefetch DBCR_ACCT_BUFFER 2932 490 1470 OPSYS 500 Not-Allowd Synonym Table User-Defined System-Calculated Total-Space Used 1000 4096 16k Allocation Initial Addit'l Num-Alloc Size-Init Size-Add'l Tot-Space 490 490 1 1.6meg 0 1.6meg Storage Stg-Pools Getmain'd Above-16mb Below-16mb Total 7k 1.6meg 1.6meg 0 1.6meg
 
DCMT DISPLAY BUFFER buffer-name AREA
 
D BUFFER DBCR_ACCT_BUFFER AREA --- Data Buffer -- Size In-use Max Getstg Prfetch-Min Prefetch DBCR_ACCT_BUFFER 2932 490 1470 OPSYS 500 Not-Allowd Synonym Table User-Defined System-Calculated Total-Space Used 1000 4096 16k Allocation Initial Addit'l Num-Alloc Size-Init Size-Add'l Tot-Space 490 490 1 1.6meg 0 1.6meg Storage Stg-Pools Getmain'd Above-16mb Below-16mb Total 7k 1.6meg 1.6meg 0 1.6meg ---------- Area ----------- Lock Lo-Page Hi-Page #Ret #Upd #Tret #Ntfy DBCR.ACCTHIST Ret 690001 740040 0 0 0 0 Stamp: 2000-07-11-04.32.28.744494 Pgrp: 15 Share NoICVI NoPerm
 
DCMT DISPLAY BUFFER buffer-name FILE
 
D BUFFER DBCR_ACCT_BUFFER FILE --- Data Buffer -- Size In-use Max Getstg Prfetch-Min Prefetch DBCR_ACCT_BUFFER 2932 Not Open 0 OPSYS Synonym Table User-Defined System-Calculated Total-Space Used 1000 0 Allocation Initial Addit'l Num-Alloc Size-Init Size-Add'l Tot-Space 490 0 -------- Data File -------- Mode Stat Pg-Size Fl-Type M-Cache S-Cache DD-Name DBCR.ACCOUNTA Ret 0 2932 non-VSAM No No ACCOUNTA Pre-fetch: Not-Allowed (DMCL) Pages per Track 16 VOLSER: TECH05 DSname: (DMCL).. DBDC.SYSTEMXX.DBCRACCA.X DISP=SHR DBCR.ACCOUNTB Ret 0 2932 non-VSAM No No ACCOUNTB Pre-fetch: Not-Allowed (DMCL) Pages per Track 16 VOLSER: CULL05 DSname: (DMCL).. DBDC.SYSTEMXX.DBCRACCB.X DISP=SHR DBCR.ACCOUNTC Ret 0 2932 non-VSAM No No ACCOUNTC Pre-fetch: Not-Allowed (DMCL) Pages per Track 16 VOLSER: CULL06 DSname: (DMCL).. DBDC.SYSTEMXX.DBCRACCC.X DISP=SHR DBCR.ACCOUNTD Ret 0 2932 non-VSAM No No ACCOUNTD Pre-fetch: Not-Allowed (DMCL) Pages per Track 16 VOLSER: CULL05 DSname: (DMCL).. DBDC.SYSTEMXX.DBCRACCD.X DISP=SHR DBCR.ACCOUNTE Ret 0 2932 non-VSAM No No ACCOUNTE Pre-fetch: Not-Allowed (DMCL) Pages per Track 16 VOLSER: CULL06 DSname: (DMCL).. DBDC.SYSTEMXX.DBCRACCE.X DISP=SHR
 
More Information
 
  • For more information about creating buffers and changing their characteristics, see documentation of the CREATE BUFFER and ALTER BUFFER statements in the 
    Database Administration documentation
    .
  • For more information about changing buffer characteristics for the current DC/UCF session, see DCMT VARY BUFFER.
  • For more information about sizing buffers, see the 
    Database Design documentation
    .
  • For more information about buffer performance considerations, see the 
    CA IDMS Database Administration documentation
    .