Hi everyone!
Thanks a ton for this brilliant discussion here!
It turned out that Nicolas was correct! I found that the CPU was broken and
not spinning at all.
With consecutive parallel query execution, the CPU temperature hits 100C
almost immediately after 1 or 2 iterations.
So the processor start
Laurenz Albe writes:
> On Tue, 2019-12-17 at 11:11 -0500, Jeff Janes wrote:
>> If it is doing a seq scan (I don't know if it is) they intentionally use a
>> small ring buffer to, so they evict their own recently used blocks, rather
>> than evicting other people's blocks. So these blocks won't bui
On Tue, 2019-12-17 at 11:11 -0500, Jeff Janes wrote:
> On Tue, Dec 17, 2019 at 8:08 AM Laurenz Albe wrote:
> > On Mon, 2019-12-16 at 15:50 -0500, Tom Lane wrote:
> > > Peter Geoghegan writes:
> > > > Why do the first and the twentieth executions of the query have almost
> > > > identical "buffers
On Tue, Dec 17, 2019 at 8:08 AM Laurenz Albe
wrote:
> On Mon, 2019-12-16 at 15:50 -0500, Tom Lane wrote:
> > Peter Geoghegan writes:
> > > Why do the first and the twentieth executions of the query have almost
> > > identical "buffers shared/read" numbers? That seems odd.
> >
> > It's repeat exe
On Mon, 2019-12-16 at 15:50 -0500, Tom Lane wrote:
> Peter Geoghegan writes:
> > Why do the first and the twentieth executions of the query have almost
> > identical "buffers shared/read" numbers? That seems odd.
>
> It's repeat execution of the same query, so that doesn't seem odd to me.
Really
Hi,
On 2019-12-16 17:48:16 -0500, Tom Lane wrote:
> Hmm, that's an interesting thought. The OP did say the CPU type,
> but according to Intel's spec page for it [1] the difference between
> base and turbo frequency is only 4.0 vs 4.2 GHz, which doesn't seem
> like enough to explain the results ..
On Mon, Dec 16, 2019 at 2:48 PM Tom Lane wrote:
> unless you suppose it actually
> throttled to below base freq, which surely shouldn't happen that fast.
> Might be worth watching the CPU frequency while doing the test though.
>
Wouldn't expect to see such linear progression if that were the cas
Nicolas Charles writes:
> Could it be that your CPUs is warming and throttling? You didn't mention the
> platform used, so I'm not sure whether it's a server or a laptop
Hmm, that's an interesting thought. The OP did say the CPU type,
but according to Intel's spec page for it [1] the difference
Could it be that your CPUs is warming and throttling? You didn't mention the
platform used, so I'm not sure whether it's a server or a laptop
Nicolas
Le 16 décembre 2019 21:50:17 GMT+01:00, Tom Lane a écrit :
>Peter Geoghegan writes:
>> Why do the first and the twentieth executions of the q
Peter Geoghegan writes:
> Why do the first and the twentieth executions of the query have almost
> identical "buffers shared/read" numbers? That seems odd.
It's repeat execution of the same query, so that doesn't seem odd to me.
This last set of numbers suggests that there's some issue with the
On Mon, Dec 16, 2019 at 9:28 AM Shijia Wei wrote:
> 1st Query:
> Buffers: shared hit=17074 read=16388
> 20th Query:
> Buffers: shared hit=17037 read=16390
Why do the first and the twentieth executions of the query have almost
identical "buffers shared/
Hi Laurenz,
Each time the identical query executes, the total number of rows selected
stays the same. The table is actually not modified between/during runs.
The query plan stays the same between fast and slow runs. Please find two
copied here:
The first one is the output of the first query in th
Shijia Wei writes:
> I am running TPC-H on recent postgresql (12.0 and 12.1).
> On some of the queries (that may involve parallel scans) I see this
> interesting behavior:
> When these queries are executed back-to-back (sent from psql interactive
> terminal), the total execution time of them incre
On Sun, 2019-12-15 at 23:59 -0600, Shijia Wei wrote:
> I am running TPC-H on recent postgresql (12.0 and 12.1).
> On some of the queries (that may involve parallel scans) I see this
> interesting behavior:
> When these queries are executed back-to-back (sent from psql interactive
> terminal), the
Hi Shijia,
If you're using fish, I suspect you're on a Mac - I don't have experience
on this platform.
Can you check with pgAdmin (3 or 4) what the server is busy doing after a
few iterations? Check for locks, as it could be a cause. Also, do you have
concurrent INSERTs?
Olivier
On Mon, Dec 16,
Hi Olivier,
I do not think that the queries are executed concurrently. The bash for
loop ensures that the next command fires only after the first returns.
Also for some 'complex' queries, even a wait-period that is longer than the
total execution time does not completely avoid this effect.
For exa
Hi Shijia,
It sounds like concurrency on the queries: the second starts before the
first ends, and so on. With a short wait in between you ensure sequential
execution. Notice that you also have the overhead of concurrent psql...
Sounds normal to me.
Best regards
Olivier
On Mon, Dec 16, 2019, 0
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