“Result Cache: Channel” Reliable Message Waits

In this earlier post, I wrote about “reliable message” waits in Oracle and how to find out more about the channel that is being waited on.  One of these waits that we’ve been seeing with some frequency is on “Result Cache: Channel”.  In some cases, these waits have been debilitating and I believe it merits its own post, in case someone else runs into this issue.

Here is an example of one issue we experienced in 11.2.0.3.  Users were reporting a slow system and in looking at session waits, we saw long wait times for the “reliable message” event. In querying GV$CHANNEL_WAITS, we saw the following waits on instance 3 of a RAC database:

select inst_id, channel, messages_published, wait_count, WAIT_TIME_USEC/1000000 wait_time_sec
from GV$CHANNEL_WAITS
order by inst_id, wait_time_sec desc;
 INST
   ID CHANNEL                                                MESSAGES_PUBLISHED WAIT_COUNT WAIT_TIME_SEC
----- ------------------------------------------------------ ------------------ ---------- -------------
. . .
    3 Result Cache: Channel                                           474745796  473767959    267825.106
    3 obj broadcast channel                                             4928144    2643616      5065.185
    3 kxfp control signal channel                                       3349090    1140344       484.500
    3 MMON remote action broadcast channel                               401055       6999       266.940
    3 RBR channel                                                        320568      37809       137.223
. . .

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Diagnosing Oracle “reliable message” Waits

Reliable Message waits are cryptic by nature.  It is a general purpose wait event that tracks many different types of channel communications within the Oracle database.  I’ve read some blogs that suggest that this is a benign wait event that can be ignored.  My experience is that they are not benign and should not be ignored.  This post will show you how to decipher these events and resolve the issue.

Here is what you might see in an AWR report:

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