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Posts Tagged ‘oracle’

oracle.net.ns.NetException: Got minus one from a read call

Posted by FatDBA on September 3, 2020

Hi Guys,

Would like to discuss one problem that I was facing today in on one of the Oracle 12c Release 1 standalone database where application team started explaining the problem that they are getting when doing application restart, specially oracle NET exception of ‘Got minus one from a read call


Caused by: java.lang.RuntimeException: java.sql.SQLException: javax.resource.ResourceException: IJ000453: Unable to get managed connection for java:/jdbc/ProdMonkeyPD
    Caused by: java.sql.SQLException: javax.resource.ResourceException: IJ000453: Unable to get managed connection for java:/jdbc/ProdMonkeyPD
    Caused by: javax.resource.ResourceException: IJ000453: Unable to get managed connection for java:/jdbc/ProdMonkeyPD
    Caused by: javax.resource.ResourceException: IJ031084: Unable to create connection
    Caused by: java.sql.SQLRecoverableException: IO Error: Got minus one from a read call
    Caused by: oracle.net.ns.NetException: Got minus one from a read call"}}
 

They were suspecting the issue with the high number of opened files on OS. The files count was too high when listing using lsof command on this RHEL7 system and the count goes down once the services are stopped. well I was able to explain the difference that exists between RHEL6 & RHEL7 when doing count using lsof. It was in RHEL7/EL7 that shows output including TID as default compared to RHEL6/OL6. Hence the number of open files count increases in RHEL7 as compared to RHEL6. So, it has nothing to do with the error that they have reported.

So, next we have checked database alert log and it was all good, all clean, no errors nothing. I immediately checked the value of “OS_AUTHENT_PREFIX” parameter as it specifies a prefix that Oracle uses to authenticate users attempting to connect to the system. Oracle simply appends this value to the beginning of user’s operating system account name and password and which it later on compares. So, it was set to its default value that is OPS$ and was set for the backward compatibility with previous versions.

So, I have two solutions for the problem

– Set “OS_AUTHENT_PREFIX” to “” (a null string), thereby eliminating the addition of any prefix to operating system account names.
– Set “tcp.validnode_checking = no” in SQLNET.ora file
This is to enable and disable valid node checking for incoming connections. If this parameter is set to yes, then incoming connections are allowed only if they originate from a node that conforms to list specified by TCP.INVITED_NODES or TCP.EXCLUDED_NODES parameters.

So, I tried with the first option and rebooted the database to make changes persistent (this parameter is static) and asked application team to give it a try again, and as expected it worked. The error or the ORACLE NET exception ‘Got minus one from a read call‘ was resolved after applying the first fix itself.

Here the second option is valid too as that also does the same thing, but one fix at a time.

Hope It Helps
Prashant Dixit

Posted in Advanced, troubleshooting | Tagged: , | Leave a Comment »

How to use “SQL Patch” technique to fix Query performance issues.

Posted by FatDBA on November 30, 2017

Hi Guys,

In my last post “How to fix SQL Plan issues using OUTLINE DATA.” where we learned how to fix wrong cost estimates by the CBO using OUTLINE DATA of optimal plan available. But there are few issues with the approach and only worked with ad-hoc statements, as failed to handle situations when

– How to deal with situations when the SQL is coming from bundled applications and cannot be modified ?
– How to look for less number of hints leading to better execution plan?
– How, if it’s not possible to use the SQL BASELINES.

As discussed in the same last post where we added the full list of OUTLINE DATA, it seems little complicated, dirty and disordered to add the full outline set to the SQL statement.
ex: select /*+ …full outline here…*/

So, how to add required set of HINTS to force the better plan for the SQL.

Lets do a test to explain this subject in detail.

SQL TEXT: select count(*) from dixit.test;
Problem Statement: Query taking huge time to complete the COUNT of rows for TEST table and doing a FULL TABLE SCAN despite of Indexes.

Now after querying the DBA_HIST_SQLSTAT view i saw a total of 2 execution plans available and query is somehow picking the wrong plan or the costliest plan.
So, lets grab the OUTLINE data of the better plan first.

select * from table(dbms_xplan.display_awr(‘SQL_ID’, PHV, format => ‘ADVANCED’));
OR
EXPLAIN PLAN for select count(*) from dixit.test;
select * from table(dbms_xplan.display(format=>’+OUTLINE’));

Outline Data
————-
/*+
BEGIN_OUTLINE_DATA
INDEX_RS_ASC(@"SEL$1" "TEST"@"SEL$1")
OUTLINE_LEAF(@"SEL$1")
ALL_ROWS
DB_VERSION('11.2.0.4')
OPTIMIZER_FEATURES_ENABLE('11.2.0.4')
IGNORE_OPTIM_EMBEDDED_HINTS
END_OUTLINE_DATA
*/

Lets create the SQL PATCH for the statement to force the SQL to use it with required number of HINTS.

begin
dbms_sqldiag_internal.i_create_patch(
sql_text => 'select count(*) from dixit.test',
hint_text => 'INDEX_RS_ASC(@"SEL$1" "STAGE"@"SEL$1")',
name => 'test_sql_patch_dixit');
end; /

I ran the query once again and as expected it ran this time with very less elapsed time and used Index Scan in place of expensive FTS.
I also noticed a new NOTE coming just below the execution plan.

Note
--------
- SQL patch "test_parallel_patch" used for this statement

In case if want to delete the patch.

begin
DBMS_SQLDIAG.DROP_SQL_PATCH(name => 'test_sql_patch_dixit');
end;
/


HOPE IT HELPS!
Prashant Dixit

Posted in Advanced | Tagged: , , , | Leave a Comment »

 
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