Affect of negative cache hits and long searches
hi my name is sumit.
In my network there is a frame-relay pvc on 7206 VXR router on which 2 T1's are terminated(from S8700 EPABX) and the bandwidth of this PVC is 600 KBPS. we are using rtp and tcp header compression technique(codec g729r8).7206 router is connected to IGX through HSSI cable and there is a IGX to IGX connectivity from INDIA to US. At US site there is a same network. and it is further connected to AT&T cloud. mainly on this PVC there is inbound traffic which comes from US AT&T cloud.
we are facing a lot of voice quality issues and when i use show frame relay ip rtp header-compression.
the counter negative cache hits and long searches rapidly increases
can somebody help me to solve the problem.
and tell me is there any affect on voice quality if these counters rapidly increases
Is there any one to answer this query..........
any update .............
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Counter negative cache hits and long searches
hi my name is sumit.
In my network there is a frame-relay pvc on 7206 VXR router on which 2 T1's are terminated(from S8700 EPABX) and the bandwidth of this PVC is 600 KBPS. we are using rtp and tcp header compression technique(codec g729r8).7206 router is connected to IGX through HSSI cable and there is a IGX to IGX connectivity from INDIA to US. At US site there is a same network. and it is further connected to AT&T cloud. mainly on this PVC there is inbound traffic which comes from US AT&T cloud.
we are facing a lot of voice quality issues and when i use show frame relay ip rtp header-compression.
the counter negative cache hits and long searches rapidly increases
can somebody help me to solve the problem.
and tell me is there any affect on voice quality if these counters rapidly increaseshi Neo thanks for reply.
r u from Datacraft ?
I am also from Datacraft
i have already used this URL. but it gives only one statement about counters.
but i am asking what could be an impact of these counters on voice ?
please reply
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I have a cache developed in-house, which implements the HashMap functionalities of get(key), put(key, object) etc, and in addition, maintains hit and miss counts. I'm trying to replace this cache with Coherence because eventually I wish to migrate to a distributed cache. It's essential, therefore, that I fit Coherence into my application in such a way that though I would currently be using Coherence's local cache functionality, later I should be able to use the distributed cache functionality without any changes to my code. Hence, I'm using CacheFactory to obtain a cache whose config I define in the coherence-config.xml file. Here's my problem: I notice that CacheFactory.getCache() returns an object that implements NamedCache. This interface does NOT support the maintenance of cache hit and miss counts. I need this functionality! How do I work around this?
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PavelPavel wrote:
Hello!
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Difference between 'Always Refresh' and 'Disable Cache Hits'
We are using clustered application servers with its own cache. We are not doing any cache synchronization. So, for selective objects we should ensure that cache is not returning stale objects.
I see two options in MWB for refreshing and disabling the cache. Can somebody explain the difference between these two and recommend what I should do to address my problem.
Thanks in advance.These are similar and often used together settings:
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Problem with the cache hit ratio
Hello,
I ma having a problem with the cache hit ratio I am geting. I am sure, 100% sure, that something has got to be wrong with the cache hit ratio I am fetching!
1) I will post the code that I am using to retrieve the cache hit ratio. I've seen about a thousand different equations, all equivalent in the end.
In oracle cache hit ratio seems to be:
cache hits / cache lookups,
where cache hits <=> logica IO - physical reads
cache lookups <=> logical IO
Now some people use the session logical Reads stat, from teh view v$sysstat; others use db block gets + db consistent gets; whatever. At the end of the day its all the same, and this is what i Use:
SELECT (P1.value + P2.value - P3.value) AS CACHE_HITS, (P1.value + P2.value) AS CACHE_LOOKUPS, P4.value AS MAX_BUFFS_SIZEB
FROM v$sysstat P1, v$sysstat P2, v$sysstat P3, V$PARAMETER P4
WHERE
P1.name = 'db block gets' AND
P2.name = 'consistent gets' AND
P3.name = 'physical reads' AND
P4.name = 'sga_max_size'
2) The problem:
The cache hit ratio I am retrieving cannot be correct. In this case i was benchamarking a HUGELY inneficient query, consisting of the Union of 5 Projections over the same source table, and Oracle is configured with a relatively small SGA of 300 MB. They query plan is awful, the database will read the source database table 5 times.
And I can see in the physical data statistics of the source tablespace, that total Bytes read is aproximatly 5 times the size of the text file that I used to bulk load data into the databse.
Some of the relevant stats, wait events:
db file scattered read 1129,93 seconds
Elapsed time: 1311,9 seconds
CPU time: 179,84
SGA max Size: 314572800 Bytes
And total bytes read: 77771964416 B (aproximatly 72 Gga bytes)
the source txt loaded to the database was aprox 16 G
Number of reads was like 4.5 times the source datafile.
I would say this, given the difference between CPU time and Elapsed Time, it is clear that the query spent almost all of its time doin DB file scattered reads. How is it possible that i get the following cache hit ratio:
Cache hit Ratio: 0,92
Cache hits: 109680186
Cache lookups: 119173819
I mean only 8% of that Logical I/O corresponded to physical I/O? It is just not possible.
3) Procedure of taking stats:
Now to retrieve these stats I snapshot the system 2 times. One before the query, one after the query.
But: this is not done in a single session. In total 3 sessions are created. One session two retrieve the stats before the query, one session to run the query, a last session to snapshot after the query.
Could the problem, assuming there is one, be related to this:
"The V$SESSTAT view contains statistics on a per-session basis and is only valid for the session currently connected. When a session disconnects all statistics for the session are updated in V$SYSSTAT. The values for the statistics are cleared until the next session uses them."
What does this paragraph mean. Does it mean that the v$sysstat only shows you the stats of the last session that closed? Or does it mean thtat v$sysstat is increamented with the statistics of each v$sessionstat once a session terminates? If so, then my procedure for gathering those stats should be correct.
Can anyone help me sort out the origin of such a high cache hit ratio, with so much I/O being done?sono99 wrote:
Hi,s
first of, let me start by saying that there were many things in your post that you mentioned that I could no understand. 1. Because i am not an Oracle Expert, i use whatever RDBMS whenever i need to. 2. Because another problem has come up and, right now, i cannot inform myself to be able to comprehend it all.Well, could it be that you need to understand the database you are working on in order to comprehend it? That is why we strongly advise you to read the concepts manual first, you need to understand the architecture that Oracle uses, as well as the basic concepts of how oracle does locking and maintains read consistency. It does these different than other database engines, and some things become nonsense if looked at from the viewpoint of a single user.
>
quote:
It would be useful to see the execution plan jhust in case you have simplified the problem so much that a critical detail is missing.
First, the query code:
2009-10-20 15:11:59,141 INFO]: OUTPUT_GOBLER:>SQL> CREATE TABLE FAVFRIEND
[2009-10-20 15:11:59,141 INFO]: OUTPUT_GOBLER:> 2 NOLOGGING TABLESPACE TARGET
[2009-10-20 15:11:59,141 INFO]: OUTPUT_GOBLER:> 3 AS
[2009-10-20 15:11:59,141 INFO]: OUTPUT_GOBLER:> 4 SELECT ID as USRID, FAVF1 as FAVF FROM PROFILE
[2009-10-20 15:11:59,141 INFO]: OUTPUT_GOBLER:> 5 UNION ALL
[2009-10-20 15:11:59,141 INFO]: OUTPUT_GOBLER:> 6 SELECT ID as USRID, FAVF2 AS FAVF FROM PROFILE
[2009-10-20 15:11:59,141 INFO]: OUTPUT_GOBLER:> 7 UNION ALL
[2009-10-20 15:11:59,141 INFO]: OUTPUT_GOBLER:> 8 SELECT ID as USRID, FAVF3 AS FAVF FROM PROFILE
[2009-10-20 15:11:59,141 INFO]: OUTPUT_GOBLER:> 9 UNION ALL
[2009-10-20 15:11:59,141 INFO]: OUTPUT_GOBLER:> 10 SELECT ID as USRID, FAVF4 AS FAVF FROM PROFILE
[2009-10-20 15:11:59,141 INFO]: OUTPUT_GOBLER:> 11 UNION ALL
[2009-10-20 15:11:59,141 INFO]: OUTPUT_GOBLER:> 12 SELECT ID as USRID, FAVF5 AS FAVF FROM PROFILE
[2009-10-20 15:11:59,141 INFO]: OUTPUT_GOBLER:> 13 ;
Now, Althought it is clear from the query that the statement is executed with the NOLOGGiNG, i have disabled the logging entirely for the tablespace.There are certain rules about nologging that may not be obvious. Again, this derives from the basic Oracle architecture, and if you use the wrong definitions of things like logging, you will be led down the primrose path to confusion.
>
Futhermore, yes, the RDBMS is a test RDBMS... I have droped the database a few times... And I am constantly deleting an re-inserting data into the source database table named PROFILE.>
I also make sure do check all the datafile statistics, and for this query the amount of RedoLog, Undo "Log", Templife used is negligible, practically zero.Create table is DDL, which has implied commits before and afterwards. There is a lot going on, some of it dependent on the volume of data returned. The Oracle database writer writes things out when it feels like it, there are situations where it might just leave it in memory for a while. With nologging, Oracle may not care that you can't perform recovery if it is interrupted. So you might want to look into statspack or EM to tell you what is going on, the datafile statistics may not be all that informative for this case.
>
Most of the I/O is reading, a few of the I/O is writing.
My idea is not to optimize this query, it is to understand how it performs. Well, have you read the Concepts manual?
I have other implementations to test, namely I having trouble with one of them.
Furthermore, I doubt the query Plan Oracle is using actually involves tablescans (as I I'd like it to do); because in the Wait Events, most of the wait time for this query is spent doing "db file scattered read". And I think this is different from a tablescan.Please look up the definition of [db file scattered read|http://download.oracle.com/docs/cd/B19306_01/server.102/b14211/instance_tune.htm#sthref703].
>
Do you really have to use sessions external to the query session ? Can you query v$mystat joined to v$statname from the session itself.
No, I don't want to that!
I avoid as much as possible having the code I execute being implemented in java. Why do you think java has anything to do with this? In your session, desc v$mystat and v$statname, these are views you can look at.
When i can avoid it I don't query the database directly through JDBC, i use the RDBMS command line client, which is supposed to be very robust. Er, is that sqlplus?
So yes, I only connect to the database with JDBC... in very last session.
Of course, I Could Have put both the gather stats before query and gathers stats after query a single script: the script that would be also runing the query.
But that would cause me a number of problems, namely some of the SQL i build has to be implemented dynamically. And I don't want to be replicating the snapshoting code into every query script I make. This way I have one sql with the snapshoting scripts; and multiple scripts for running each query. I avoid code replication in this manner.Instrumentation is a large subject; dynamic sql generation is something to be avoided if possible. Remember, Oracle is written with the idea that many people are going to be sharing code and the database, so it is optimized in that way. For SQL parsing in particular, if every SQL is different, you get a performance problem called "hard parsing." You can (and generally should, and sometimes can't avoid) use bind variables so that Oracle doesn't need to hard parse every SQL. In fact, this is one of those things that applies to other engines besides Oracle. I would recommend you read Tom Kyte's books, he explains what is going on in detail, including in some places the non-Oracle viewpoint.
>
Furthermore, Since the database is not a production database, it is there so I can do my tests. I don't have to be concerned with what other sessions may be doing to my system. There are only the sessions I control.No, there are sessions Oracle controls. If you are on unix, you can easily see this, but there are ways to see it on Windows, too. In some cases, your own sessions can affect themselves.
>
then what it the array fetch size ? If the array fetch size is large enough the number of block visits would be similar to the number of physical block reads.
I don't know what the arraysize you mention is. i have not touched that parameter. So whatever it is, it's the default.You should find out! You can go to http://tahiti.oracle.com and type array fetch size into the search box. You can also go to http://asktom.oracle.com and do the same thing, with some more interesting detail.
>
By the way, I don't get the query results into my client, the query results are dumped into a target output table.
So, if the arraysize has something to do with the number of rows that Oracle is returning the client in each step... I think it doesn't matter.You may hear this phrase a lot:
"It depends."
>
As for the query plan, If i am not mistaken you can't get get query plans for queries that are: create table as select.What?
JG@TTST> explain plan for create table jjj as select * from product_master;
Explained.
JG@TTST> select count(*) from plan_table;
COUNT(*)
3
I can however commit the create table part and just call for the evalution of the Select part of the query; i believe it should be same.
"Optimizer" "Cost" "Cardinality" "Bytes" "Partition Start" "Partition Stop" "Partition Id" "ACCESS PREDICATES" "FILTER PREDICATES"
"SELECT STATEMENT" "ALL_ROWS" "2563" "586110" "15238860" "" "" "" "" ""
"UNION-ALL" "" "" "" "" "" "" "" "" ""
"TABLE ACCESS(FULL) SONO99.PROFILE" "" "512" "117222" "3047772" "" "" "" "" ""
"TABLE ACCESS(FULL) SONO99.PROFILE" "" "513" "117222" "3047772" "" "" "" "" ""
"TABLE ACCESS(FULL) SONO99.PROFILE" "" "513" "117222" "3047772" "" "" "" "" ""
"TABLE ACCESS(FULL) SONO99.PROFILE" "" "513" "117222" "3047772" "" "" "" "" ""
"TABLE ACCESS(FULL) SONO99.PROFILE" "" "513" "117222" "3047772" "" "" "" "" ""
This query plan was taken from sql developer, exported to txt, and the PROFILE table here has only 100k tuples.
Right now I am more concerned with testing the MODEL query. Which Oracle doesn't seem to be able any more... but that is a matter for another thread.
Regarding this plan. The Union ALL seems to be more than just a binary Operator... IT seems to be Neray.
The union all on that execution plan seems to be taking as leaf tables 5 99sono.Profile tables, and be making a table scan to them all. So I'd say that the RDBMS should only scan each database block once and not 5 times.
But: It doesn't seem to be so. IT seems like what oracle is doing is scanning completly each the table, and then moving on to next select statement in the UNION ALL. Because given the amount of source table that was read, 5 times greater than the size of the source table. Oracle didn't reuse read blocks.
But this is just my feeling.Your feeling is uninteresting. Telling us what you really hope to accomplish might be more interesting.
Anyway, in terms of consistent gets, how many consistent gets should the RDBMS be doing? 5
One for each table block?It depends.
>
My best regards,
Nuno (99sono xp).
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