SQL*Net message from client

Sql*net message from client is generally considered an idle event as the Oracle server process is waiting for the client process. Some dbas do not pay any attention to this event. It is good this seems to be changing.

This case i have come into shows the importance of this event.
User queries a simple base block form which gets one row from a table (which contains that single row), changes one column and commits the change. The user is complaining about the performance of this form and says he always waits 5-6 seconds for this update. The sql trace for this session shows the following sql statements:

Select row from table;
Select row from table where rowid=:1 for update;
Update table set col=value where rowid=:2;

Each sql statement’s statistics show that all their elapsed times were 0.00. But here are the totals at the end of the trace file:

OVERALL TOTALS FOR ALL NON-RECURSIVE STATEMENTS

call     count       cpu    elapsed       disk      query    current        rows
------- ------  -------- ---------- ---------- ---------- ----------  ----------
Parse        4      0.01       0.00          0          0          0           0
Execute      7      0.00       0.01          0          0          0           1
Fetch        5      0.00       0.00          0         12          0           5
------- ------  -------- ---------- ---------- ---------- ----------  ----------
total       16      0.01       0.02          0         12          0           6

Misses in library cache during parse: 0

Elapsed times include waiting on following events:
  Event waited on                             Times   Max. Wait  Total Waited
  ----------------------------------------   Waited  ----------  ------------
  SQL*Net message to client                     172        0.00          0.00
  SQL*Net message from client                   172        0.68          6.20
  latch free                                      1        0.00          0.00
  SQL*Net message to dblink                       8        0.00          0.00
  SQL*Net message from dblink                     8        0.00          0.01
  log file sync                                   1        0.00          0.00

Here we see why he is talking about the 5 seconds response time of this simple form. Sql*net message from client waits account for 6 seconds of elapsed time. There are 172 waits for this event. Surely any other action than reducing sql*net message from clients here can not make any improvements in performance. When we quit using base block and populating the block using a “select col_list into ... “ statement and then updating the row, we reduced the number of sql*net message from clients from 172 to 36 and response time from 6.20 sec to 1 sec.