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12 Replies Latest reply: Jan 24, 2013 5:04 AM by bas_ua RSS

instance throughput rate

bas_ua Newbie
Currently Being Moderated
Hi!

Explain me please, how it could be…
In OEM “Instance throughput rate” "physical reads(Kb)" shows much greater numbers than shows “IO” tab “I/O Megabytes per second by I/O Function” “Direct reads” at the same time?
  • 1. Re: instance throughput rate
    Mihael Pro
    Currently Being Moderated
    Explain me please, how it could be…
    In OEM “Instance throughput rate” "physical reads(Kb)" shows much greater numbers than shows “IO” tab “I/O Megabytes per second by I/O Function” “Direct reads” at the same time?
    "physical reads" occurs when database reads from disk to buffer cache or bypassing buffer cache
    "direct reads" occurs when database reads from disk bypassing buffer cache
  • 2. Re: instance throughput rate
    bas_ua Newbie
    Currently Being Moderated
    I don't see much db cache reads at the time I talking about. Almost all reads - Direct reads. For example Direct reads = 40 MBps, Buffer cache reads = 5 MBps. But Throughput physical reads shows at the same time up to 160 MBps?
  • 3. Re: instance throughput rate
    Mihael Pro
    Currently Being Moderated
    I don't see much db cache reads at the time I talking about. Almost all reads - Direct reads. For example Direct reads = 40 MBps, Buffer cache reads = 5 MBps. But Throughput physical reads shows at the same time up to 160 MBps?
    "physical reads" is all reads from disk, including "Buffer cache reads", "Direct reads" etc.
  • 4. Re: instance throughput rate
    bas_ua Newbie
    Currently Being Moderated
    "etc." < 1MBps
    40 MBps + 5 MBps + "etc" < 160 MBps.

    By the way, nmon shows numbers close to Direct reads, not "Throughput physical reads".
  • 5. Re: instance throughput rate
    Mihael Pro
    Currently Being Moderated
    "etc." < 1MBps
    40 MBps + 5 MBps + "etc" < 160 MBps.

    By the way, nmon shows numbers close to Direct reads, not "Throughput physical reads".
    use the following query :

    select name, value from v$sysstat where name like 'physical reads%' order by name;
  • 6. Re: instance throughput rate
    bas_ua Newbie
    Currently Being Moderated
    select name, value from v$sysstat where name like 'physical reads%' order by name;

    NAME VALUE
    ---------------------------------------------------------------- ----------
    physical reads 943387011
    physical reads cache 142015877
    physical reads cache prefetch 70935370
    physical reads direct 801371134
    physical reads direct (lob) 46372479
    physical reads direct temporary tablespace 5137998
    physical reads for flashback new 0
    physical reads prefetch warmup 372830
    physical reads retry corrupt 0
  • 7. Re: instance throughput rate
    Mihael Pro
    Currently Being Moderated
    select name, value from v$sysstat where name like 'physical reads%' order by name;

    NAME VALUE
    ---------------------------------------------------------------- ----------
    physical reads 943387011
    physical reads cache 142015877
    physical reads cache prefetch 70935370
    physical reads direct 801371134
    physical reads direct (lob) 46372479
    physical reads direct temporary tablespace 5137998
    physical reads for flashback new 0
    physical reads prefetch warmup 372830
    physical reads retry corrupt 0
    So, direct reads are most reads, this can be result of Parallel Query.
  • 8. Re: instance throughput rate
    Harsh_v Newbie
    Currently Being Moderated
    According to you.................

    "physical reads" occurs when database reads from disk to buffer cache or bypassing buffer cache
    "direct reads" occurs when database reads from disk bypassing buffer cache.


    I which condition Oracle Read "Direct reads" ? and in which "Physical Reads" ?
  • 9. Re: instance throughput rate
    Mihael Pro
    Currently Being Moderated
    Harshit -{A&amp;amp;amp;gt; wrote:
    According to you.................

    "physical reads" occurs when database reads from disk to buffer cache or bypassing buffer cache
    "direct reads" occurs when database reads from disk bypassing buffer cache.


    I which condition Oracle Read "Direct reads" ? and in which "Physical Reads" ?
    Read all posts in this thread, please. "Physical Reads" are total reads from disk and include "Direct reads".

    select name from v$statname where name like 'physical reads%' order by name;

    there is
    "physical reads cache" - physical reads to buffer cache
    "physical reads direct" - direct reads, used, for example, in Parallel Query
  • 10. Re: instance throughput rate
    bas_ua Newbie
    Currently Being Moderated
    The question I wish to answer isn't "Direct reads" or "Physical reads" itself! I know the the root course of these one (PQ, FTS, LOB)...
    But I just curiose of Oracle Enterprise Manager realtime statistics that apear in "Instance throughput tab".
    Specifically - "Instance throughput rate -> Physical reads(Kb)" and "I/O -> I/O Megabytes per Second by I/O Function". Open OEM dbconsole and look at Perfromance page.
    I think that "Physical reads" "Instance throughput rate" tab must be equal to sum of I/O "Direct reads" and "Buffer cache reads"... But they are NOT equal. So what it means?
  • 11. Re: instance throughput rate
    Mihael Pro
    Currently Being Moderated
    Okay. Currently I have no "EM" console available. I suggest open thread in "Enterprise Manager" forum.
  • 12. Re: instance throughput rate
    bas_ua Newbie
    Currently Being Moderated
    Ok. thank you.

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