Saturday, February 6, 2010

Oracle: SQL*Net Waits

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Introduction




Unfortunately, what Oracle calls "Network Waits" have little to do with Network but and almost exclusively to do with the time it takes to pack messeges for the network before they are sent.

Client = you, the tool, sqlplus, application
the shadow process is communicating to the client

Of the three waits, only "more data" is possibly related to network issues and that's not even clear, the other two are simply the time it takes to pack a message before sending it.

SQL*Net message to client - time to pack a message (no network time included) possibly tune SDU
SQL*Net more data from client - possible network issues, possibly tune SDU
SQL*Net more data to client - time to pack a message (no network time included) possibly tune SDU

The same events exist, but where the client is the shadow process and another database plays the roll of shadow process:

SQL*Net message to dblink
SQL*Net more data from dblink - possible network issues, possibly tune SDU
SQL*Net more data to dblink

SQL*Net Wait Events


SQL*Net message from client



Idle Event
Waiting for work from Client
Includes network transmission times for messages coming from shadow
Typically indicative of Client “think time” or “processing time”

SQL*Net message to client



Time it takes to pack a message to be sent to the client
Doesn’t include network timing
see Tanel Poder's analysis of SQL*Net message to client

SQL*Net more data to client

Same as SQL*Net message to client except this is for data that spans SDU packets.
Wait represents the time it takes to pack data.
Doesn’t include network timing

SQL*Net more data from client



The only SQL*Net wait that can indicate a possible NETWORK problem
Client is sending data to shadow that spans packets (think large data inserts, possibly large code blocks, large SQL statements)
Shadow waits for next packet.
Can indicate network latency.
Can indicate a problem with the client tool

Here is an example with ASHMON where the application server died mid-stream on inserts. The shadow processes were left waiting for completion of the message. You can see the regular load on the database on the left, then just past the middle the load crashes, and all that's left is waits on "SQL*Net more data from client"



Possibly set SDU=32768 as well as setting RECV_BUF_SIZE and SEND_BUF_SIZE to 65536.

SQL*Net break/reset to client

Error in sql statement
Control C
Usually highlights and error in application

Example:

CREATE TABLE T1 (C1 NUMBER);
ALTER TABLE T1 ADD
(CONSTRAINT T1_CHECK1 CHECK (C1 IN ('J','N')));
ALTER SESSION SET EVENTS
'10046 TRACE NAME CONTEXT FOREVER, LEVEL 12';
INSERT INTO T1 VALUES (1);

Trace File

PARSING IN CURSOR #2 len=25 dep=0 uid=0 oct=2 lid=0 tim=5009300581224 hv=9816834
09 ad='8e6a7c10'
INSERT INTO T1 VALUES (1)
END OF STMT
PARSE #2:c=0,e=2770,p=0,cr=2,cu=0,mis=1,r=0,dep=0,og=1,tim=5009300581220
BINDS #2:
EXEC #2:c=0,e=128,p=0,cr=0,cu=0,mis=0,r=0,dep=0,og=1,tim=5009300581418
ERROR #2:err=1722 tim=512952379
WAIT #2: nam='SQL*Net break/reset to client' ela= 31 driver id=1650815232 break?
=1 p3=0 obj#=-1 tim=5009300581549
WAIT #2: nam='SQL*Net break/reset to client' ela= 92 driver id=1650815232 break?
=0 p3=0 obj#=-1 tim=5009300581662

DBLINK SQL*Net Waits



These waits are the same as

SQL*Net message to dblink
SQL*Net more data from dblink
SQL*Net more data to dblink
SQL*Net break/reset to dblink

Analysis and Tuning

There isn't much to do on the Oracle side for tuning. You can try optimizing the SDU and SEND_BUF_SIZE and RECV_BUF_SIZE.
For actually getting information on network speeds you will have to use something like
  • ping
  • tnsping
  • network sniffe

SDU

The default SDU can be set in the sqlnet. ora
If it's not set, the default is 2048
The max is 32768
The default,or the value in sqlnet.ora, can be overridden in the tnsnames. ora and the listener.ora. The client and server negotiate the size aggreeing on the smaller of the two settings.
(TDU – Transmission Data Unit – see note 44694.1 The TDU parameter has been deprecated in the Oracle Net v8.0 and beyond and is ignored. It is only mentioned here for backward compatibility.)


tnsnames.ora

V10G = (DESCRIPTION =
(SDU=32768)
(ADDRESS = (PROTOCOL = TCP)(HOST = fuji)(PORT = 1522))
(CONNECT_DATA =
(SERVER = DEDICATED) (SERVICE_NAME = v10g)
) )

listener.ora

SID_LIST_LISTENER =
(SID_LIST =
(SID_DESC =
(SDU=32768)
(SID_NAME = v10g)
(ORACLE_HOME = /export/home/oracle10)
))

Tracing

sqlnet.ora

trace_level_client=16
trace_directory_client=/tmp
trace_file_client=client.trc
trace_unique_client = true
trace_level_server=16
trace_directory_server=/tmp
trace_file_server=server.trc

client.trc

client_3582.trc:[12-JAN-2008 11:37:39:237] nsconneg: vsn=313, gbl=0xa01, sdu=32768, tdu=32767


RECV_BUF_SIZE and SEND_BUF_SIZE

The recommended size for these buffers (from Oracle's docs) is at least

Network bandwidth * roundtrip = buffer min size

For example if the network bandwidth is 100mbs and the round trip time (from ping) is 5ms then

100,000,000 bits 1 byte 5 seconds
---------------- x ------ x --------- = 62,500 bytes
1 second 8 bits 1000


tnsnames.ora

V10G = (DESCRIPTION =
(SEND_BUF_SIZE=65536)
(RECV_BUF_SIZE=65536)
(ADDRESS = (PROTOCOL = TCP)(HOST = fuji)(PORT = 1522))
(CONNECT_DATA =
(SERVER = DEDICATED) (SERVICE_NAME = v10g)
) )

listener.ora

SID_LIST_LISTENER =
(SID_LIST =
(SID_DESC =
(SEND_BUF_SIZE=65536)
(RECV_BUF_SIZE=65536)
(SID_NAME = v10g)
(ORACLE_HOME = /export/home/oracle10)
))


sqlnet.ora

RECV_BUF_SIZE=65536
SEND_BUF_SIZE=65536

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