GT.M processes a GDS file using predominantly low-level system services. The GDS file consists of two parts:

All GT.M components, except GDE, (the run-time system, DSE, LKE, MUPIP) use the data elements of the file header for accounting, control, and logging purposes.

The current state of the file header always determines the characteristics of the database. The MUPIP CREATE command initializes the values of the file header data elements from the global directory and creates a new .DAT file.

The file header data elements are listed as follows in alphabetical order for easier access, rather than the order in which they appear in the file header.

Data Elements

Description

Access method

The buffering strategy of the database. Access Method can have 2 values - BG or MM. The default value is BG.

Buffered Global (BG) manages the buffers (the OS/file system may also buffer "in series"); MM - the OS/file system manages all the buffering.

Async IO

Whether the database file uses Asynchronous or Syncrhonous I/O. For additional information, see Chapter 4: “Global Directory Editor.

Block size (in bytes)

The size (in bytes) of a GDS block. Block size can have values that are multiples of 512. The default value is 1024. Block size should be a multiple of the native block size for the OS file system chosen to accommodate all but outlying large records. For additional information, see Chapter 4: “Global Directory Editor.

Blocks to Upgrade

The count of the blocks in the database that are still in prior major version format. GT.M uses this element during incremental upgrades.

Cache freeze id

The process identification number (PID) of a process which has suspended updates to the segment.

Certified for Upgrade to V5

Count of blocks "pre-certified" (with the dbcertify utility) for an incremental upgrade. GT.M uses this element during incremental upgrades.

Create in progress

Create in progress is TRUE only during the MUPIP CREATE operation. The normal value is FALSE.

Collation Version

The version of the collation sequence definition assigned to this database. DSE only reports this if an external collation algorithm is specified.

Commit Wait Spin Count

COMMITWAIT_SPIN_COUNT specifies the number of times a GT.M process waiting for control of a block to complete an update should spin before yielding the CPU when GT.M runs on SMP machines.

Current transaction

The 64-bit hexadecimal number of the most recent database transaction.

DB is auto-created

Indicates whether the database file is automatically created.

DB shares gvstats

Indicates whether the database supports sharing of statistics.

Default Collation

The collation sequence currently defined for this database. DSE only reports this if an external collation algorithm is defined.

Desired DB Format

The desired version format of database blocks. Desired DB Format can have 2 possible values- the major version for the current running GT.M distribution or the last prior major version. Newly created databases and converted databases have the current major version.

Endian Format

The Endian byte ordering of the platform.

Extension Count

The number of GDS blocks by which the database file extends when it becomes full. The default value is 100 and the maximum is 65535. In production, typically this value should reflect the amount of new space needed in a relatively long period (say a week or a month). UNIX file systems use lazy allocations so this value controls the frequency at which GT.M checks the actual available space for database expansion in order to warn when space is low.

Flush timer

Indicates the time between completion of a database update and initiation of a timed flush of modified buffers. The default value is 1 second and the maximum value is 1 hour.

Flush trigger

The total number of modified buffers that trigger an updating process to initiate a flush. The maximum and default value is 93.75% of the global buffers; the minimum is 25% of the global buffers. For large numbers of global buffers, consider setting the value towards or at the minimum.

Free blocks

The number of GDS blocks in the data portion of the file that are not currently part of the indexed database (that is, not in use). MUPIP INTEG -NOONLINE (including -FAST) can rectify this value if it is incorrect.

Free space

The number of currently unused blocks in the fileheader (for use by enhancements).

Global Buffers

The number of BG buffers for the region. It can have values that are multiples of 512 (in bytes). The minimum value is 64 and the maximum is 2147483647 (may vary depending on your platform). The default value is 1024. In a production system, this value should typically be higher.

In critical section

The process identification number (PID) of the process in the write-critical section, or zero if no process holds the critical section.

Journal Alignsize

Specifies the number of 512-byte-blocks in the alignsize of the journal file. DSE only reports this field if journaling is ENABLED (or ON).

If the ALIGNSIZE is not a perfect power of 2, GT.M rounds it up to the nearest power of 2.

The default and minimum value is 4096. The maximum value is 4194304 (=2 GigaBytes).

A small alignsize can make for faster recover or rollback operations, but makes less efficient use of space in the journal file.

Journal Allocation

The number of blocks at which GT.M starts testing the disk space remaining to support journal file extensions. DSE only reports this field if journaling is ENABLED or ON.

Journal AutoSwitchLimit

The number of blocks after which GT.M automatically performs an implicit online switch to a new journal file. DSE only reports this field if journaling is ENABLED or ON.

The default value for Journal AutoSwitchLimit is 8386560 & the maximum value is 8388607 blocks (4GB-512 bytes). The minimum value is 16384. If the difference between the Journal AutoSwitchLimit and the allocation value is not a multiple of the extension value, GT.M rounds-down the value to make it a multiple of the extension value and displays an informational message.

Journal Before imaging

Indicates whether or not before image journaling is allowed; DSE only reports this field if journaling is ENABLED or ON.

Journal Before imaging can either be TRUE or FALSE.

Journal Buffer Size

The amount of memory allotted to buffer journal file updates. The default value is 2312. The minimum is 2307 and the maximum is 1Mi blocks which means that the maximum buffer you can set for your journal file output is 512MB. Larger journal buffers can improve run-time performance, but they also increase the amount of information at risk in failure. Journal Buffer size must be large enough to hold the largest transaction.

Journal Epoch Interval

The elapsed time interval between two successive EPOCHs in seconds. An EPOCH is a checkpoint, at which all updates to a database file are committed to disk. All journal files contain epoch records. DSE only reports this field if journaling is ENABLED or ON.

The default value is 300 seconds (5 minutes). The minimum is 1 second and the maximum value is 32,767 (one less than 32K) seconds, or approximately 9.1 hours. Longer Epoch Intervals can increase run-time performance, but they can also cause longer recovery times.

Journal Extension

The number of blocks used by GT.M to determine whether sufficient space remains to support continuing journal file growth. DSE only reports this field if journaling is ENABLED or ON.

The default value is 2048 blocks. The minimum is zero (0) blocks and the maximum is 1073741823 (one less than 1 giga) blocks. In production, this value should typically be either zero (0) to disable journal extensions and rely entirely on the Journal Allocation, or it should be large. In UNIX, this value serves largely to allow you to monitor the rate of journal file growth.

UNIX file systems use lazy allocations so this value controls the frequency at which GT.M checks the actual available space for journal file expansion in order to warn when space is low.

Journal File

The name of the journal file. DSE only reports this field if journaling is ENABLED or ON.

Journal State

Indicates whether journaling is ON, OFF, or DISABLED (not allowed).

Journal Sync IO

Indicates whether WRITE operation to a journal file commits directly to disk. The default value is FALSE.

DSE only reports this field if journaling is ENABLED (or ON).

Journal Yield Limit

The number of times a process needing to flush journal buffer contents to disk yields its timeslice and waits for additional journal buffer content to be filled-in by concurrently active processes, before initiating a less than optimal I/O operation.

The minimum Journal Yield Limit is 0, the maximum Journal Yield Limit is 2048.

The default value for Journal Yield Limit is 8. On a lightly loaded system, a small value can improve run-time performance, but on actively updating systems a higher level typically provides the best performance.

KILLs in progress

The sum of the number of processes currently cleaning up after multi-block KILLs and the number of Abandoned KILLs.

[Note]Note

Abandoned KILLs are associated with blocks incorrectly marked busy errors.

Last Bytestream Backup

The transaction number of the last transaction backed up with the MUPIP BACKUP -BYTESTREAM command.

Last Database Backup

The transaction number of the last transaction backed up with the MUPIP BACKUP -DATABASE command. (Note -DATABASE is the default BACKUP type.)

Last Record Backup

Transaction number of last MUPIP BACKUP -RECORD or FREEZE -RECORD command.

LOCK shares DB critical section

Whether LOCK activity shares the resource manager for the database or has a separate and different critical section manager.

Lock space

A hexadecimal number indicating the 512 byte pages of space dedicated to LOCK information.

The minimum Lock space is 10 pages and the maximum is 65,536 pages. The default is 40 pages. In production with an application that makes heavy use of LOCKs, this value should be higher.

Master Bitmap Size

The size of the Master Bitmap. The current Master Bitmap Size of V6 format database is 496 (512 byte blocks).

Maximum key size

The minimum key size is 3 bytes and the maximum key size is 1019 bytes. For information on setting the maximum key size for your application design, refer to Global Directory Editor.

Maximum record size

The minimum record size is zero. A record size of zero only allows a global variable node that does not have a value. The maximum is 1,048,576 bytes (1MiB). The default value is 256 bytes.

GT.M issues an error if you decrease and then make an attempt to update nodes with existing longer records.

Maximum TN

The maximum number of TNs that the current database can hold. For a database in V7 format, the default value of Maximum TN is 0xFFFFFFF803FFFFFF.

Maximum TN Warn

The transaction number after which GT.M generate a warning and update it to a new value. The default value of Maximum TN Warn is 0xFFFFFFD813FFFFFF.

Modified cache blocks

The current number of modified blocks in the buffer pool waiting to be written to the database.

Mutex Hard Spin Count

The number of attempts to grab the mutex lock before initiating a less CPU-intensive wait period. The default value is 128.

Mutex Sleep Spin Count

The number of timed attempts to grab the mutex lock before initiating a wait based on interprocess wake-up signals. The default value is 128.

Mutex Spin Sleep Time

The number of milliseconds to sleep during a mutex sleep attempt. The default value is 2048.

No. of writes/flush

The number of blocks to write in each flush. The default value is 7.

Null subscripts

"ALWAYS" if null subscripts are legal. "NEVER" if they are not legal and "EXISTING" if they can be accessed and updated, but not created anew.

Number of local maps

(Total blocks + 511)\512.

Online Backup NBB

Block to which online backup has progressed. DSE displays this only when an online backup is currently in progress.

Reference count

The number of GT.M processes and utilities currently accessing that segment on a given node

Note: GT.M does not rely on this field. A database segment initially has a reference count of zero. When a GT.M process or utility accesses a segment, GT.M increments the reference count. GT.M decrements the reference count upon termination.

GT.M counts DSE as a process. When examining this field with DSE, the reference count is always greater than zero. When DSE is the only process using a region, the reference count should be one.

Region Seqno

The current replication relative time stamp for a region.

Replication State

Either On or OFF. [WAS ON] OFF means that replication is still working, but a problem with journaling has caused GT.M to turn it off, so GT.M is still replicating, but will turn replication OFF if it ever has to turn to the journal because the pool has lost data needed for replication.

Reserved Bytes

Number of bytes reserved in database blocks.

Starting VBN

Virtual Block Number of the first GDS block after the GDS file header; this is block 0 of the database and always holds the first local bitmap.

Timers pending

Number of processes considering a timed flush.

Total blocks

Total number of GDS blocks, including local bitmaps.

WIP queue cache blocks

The number of blocks for which GT.M has issued writes that have not yet complete.

Wait Disk

Seconds that GT.M waits for disk space to become available before it ceases trying to flush a GDS block's content to disk. During the wait, it sends eight (8) approximately evenly spaced operator log messages before finally issuing a WAITDSKSPACE error. For example, if Wait Disk is 80 seconds and GT.M finds no disk space to flush a GDS block, it sends a WAITDSKSPACE syslog message about every 10 seconds, and after the eighth message issues a WAITDSKSPACE error. This field is only used in UNIX because of its reliance on lazy disk space allocation.

Zqgblmod Seqno

The replication sequence number associated with the $Zqgblmod() Transaction number.

Zqgblmod Trans

Transaction number used by the $ZQGBLMOD() function in testing whether a block was modified by overlapping transactions during a replication switchover.

Average Blocks Read per 100 Records

Acts as a clue for replication update helper processes as to how aggressively they should attempt to prefetch blocks. It's an estimate of the number of database blocks that GT.M reads for every 100 update records. The default value is 200. For very large databases, you can increase the value up to 400.

Update Process Reserved Area

An approximate percentage (integer value 0 to 100) of the number of global buffers reserved for the update process. The reader helper processes leaves at least this percentage of the global buffers for the update process. It can have any integer value between 0 to 100. The default value is 50.

Pre read trigger factor

The percentage of Update Process reserved area after which the update process processes signals the reader helper processes to resume processing journal records and reading global variables into the global buffer cache. It can have any integer value between 0 to 100. The default value is 50.

Update writer trigger factor

One of the parameters used by GT.M to manage the database is the flush trigger. One of several conditions that triggers normal GT.M processes to initiate flushing dirty buffers from the database global buffer cache is when the number of dirty buffers crosses the flush trigger. In an attempt to never require the update process itself to flush dirty buffers, when the number of dirty global buffers crosses the update writer trigger factor percentage of the flush trigger value, writer helper processes start flushing dirty buffers to disk. It can have any integer value between 0 to 100. The default value is 33, that is, 33%.

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