6.12.14 Determining the size of user logs that are required for the maintenance processing of the updated-row columnizing facility (variable max_user_log)
Before you enable the updated-row columnizing facility, determine the size of user logs that are required for the maintenance processing of the updated-row columnizing facility.
The maintenance processing of the updated-row columnizing facility is performed for each chunk of a column store table. Therefore, first, determine the size of user logs (COLUMNIZELOG) for each chunk of the column store table to which the updated-row columnizing facility is applied. Then, use the largest determined size as the size of user logs that are required for the maintenance processing of the updated-row columnizing facility. Use the following formula to determine the size of user logs (COLUMNIZELOG) for each chunk.
Formula (bytes)
COLUMNIZELOG = 1,428
+ (rowdata_sgmt_num × 112 + var_sgmt_num × 1,428
+ dbarea_file_num × SEGSIZE × 144) × COMPRESSION_RATE
+ dbarea_file_num × 2,080
Explanation of variables
- rowdata_sgmt_num
-
Number of row-data segments for which the maintenance processing of the updated-row columnizing facility is performed
Determine the number of row-data segments in the chunk by referring to the explanation of the variable UPDATESEGNUM(i) in (g) Determining the variable SGCOLUMNTBL (for a multi-chunk table) in (2) Explanation of variables in 5.8.1 Determining the total number of pages in the data DB area.
- var_sgmt_num
-
Number of segments used to store the branch rows that are created
Determine the value by referring to the following variable explanation on the assumption that the data added or updated by the INSERT or UPDATE statement in the chunk is imported by using the adbimport command:
- dbarea_file_num
-
Number of DB area files in the DB area in which the column store table is to be stored
- SEGSIZE
-
Segment size (pages)
Use the following formula to determine this value:
SEGSIZE = 4,194,304 ÷ page_size
- page_size
-
Page size of data DB area (bytes)
- COMPRESSION_RATE
-
Compression rate of source data
Determine the value by referring to the explanation of the variable COMPRESSION_RATE in (g) Determining the variable SGCOLUMNTBL (for a multi-chunk table) in (2) Explanation of variables in 5.8.1 Determining the total number of pages in the data DB area.
If the compression rate is unknown, assume 0.5.