Progress
Database Administration
Guide and Reference


PROMON Block Access Option

Displays database buffer pool access statistics. Figure 19–6 shows an example of this option’s output.

        Block Access: 
                            DB      DB    DB     BI    BI     AI    AI 
        Type Usr Name       Reqst   Read  Write  Read  Write  Read  Write 
        Acc  999 TOTAL...   17393   1866    424   321    989   204    444 
        Acc    0              102    102     34    23     75    12     48 
        Acc    1 sue         6060    876    144   165    304    75    128 
        Acc    2 dave        4023    654    185    78    406    34    156 
        Acc    3               86     84      8    12     22     9     18 
        Acc    4 mary        3454      6     13     7     46     3      6 
        Acc    5 bill        3726    235     58    43    128    28     71 
        Acc    6                0      0      0     0      0     0      0 
RETURN - repeat, U - continue uninterrupted, Q - quit: 

Figure 19–6: Sample Output For PROMON Block Access Option

The first line displays cumulative information for all users. The six read and write columns refer to disk I/O. Reads and writes are always one block. Block size varies among systems, but is usually 512 bytes, 1,024 bytes, or 2,048 bytes.

DISPLAY FIELDS
Type

This column always has the value Acc.

Usr

The user number of the process.

Name

For client processes, the user name.

DB Reqst

The number of times the database buffer system was searched to find a block. The buffer system is searched every time a process attempts to access a record. If the block that holds the desired record is already in memory, a disk read is not required. If the ratio of DB Reqst to DB Read is not high (10 to 1 or greater), consider raising the value of the Blocks in Database Buffers (-B) startup parameter. Regardless of the number of available buffers, random record access causes a lower database request to disk read ratio than sequential record access.

DB Read

The number of database disk block reads. A database block must be read from disk when a process accesses a record whose containing block is not already in the database buffers. Recall that for read-only database requests, Progress uses private database buffers if they are available, rather than the shared buffer pool (allocated with the Blocks in Database Buffers (-B) parameter).

DB Write

The number of database block writes to disk. Once the database buffers are full, every disk read overwrites an existing block; if the overwritten block has been modified since it was read in, it must be written to disk. This accounts for the majority of block writes.

BI Read

The number of before-image (BI) file block reads. For example, the BI file is read when a transaction is undone. The BI file has its own one-block input buffer and does not use the database buffer pool.

BI Write

The number of BI file block writes. When a record is updated, a pretransaction copy of the record is written to the BI file. When the transaction completes, the database engine writes the last BI file block out to disk (assuming you are running the database with full integrity). This post-transaction disk write accounts for the relatively high number of BI file writes, but it can be delayed with the Delay BI File Write (-Mf) startup parameter.

In addition to record images, the database engine writes to the BI file various notes and data required to reconstruct a damaged database. The BI file has its own one-block output buffer and does not use the shared database buffer pool.

AI Read

The number of after-image (AI) file block reads. The AI file is read during crash recovery. The AI file has a one-block input/output buffer and does not use the database buffer pool.

AI Write

The number of AI file block writes. When you run the database with after-imaging enabled, a copy of each note written to the BI file is written to the AI file.


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