Estimating logical-log size when logging dbspaces

To estimate the size of logical logs, use a formula or onstat -u information.

Use the following formula to obtain an initial estimate for LOGSIZE in kilobytes: 
LOGSIZE = (connections * maxrows * rowsize) / 1024) / LOGFILES

In this formula:

  • connections is the maximum number of connections for all network types specified in the sqlhosts information by one or more NETTYPE parameters. If you configured more than one connection by setting multiple NETTYPE configuration parameters in your configuration file, sum the users fields for each NETTYPE parameter, and substitute this total for connections in the preceding formula.
  • maxrows is the largest number of rows to be updated in a single transaction.
  • rowsize is the average size of a row in bytes. You can calculate rowsize by adding up the length (from the syscolumns system catalog table) of the columns in a row.
  • 1024 is a necessary divisor because you specify LOGSIZE in kilobytes.

To obtain a better estimate during peak activity periods, execute the onstat -u command. The last line of the onstat -u output contains the maximum number of concurrent connections.

You need to adjust the size of the logical log when your transactions include simple large objects or smart large objects, as the following sections describe.

You also can increase the amount of space devoted to the logical log by adding another logical-log file.