Re: A little COPY speedup

Simon Riggs wrote:
> On Thu, 2007-03-01 at 17:01 +0000, Heikki Linnakangas wrote:
>
>> I ran oprofile on a COPY FROM to get an overview of where the CPU time
>> is spent. To my amazement, the function at the top of the list was
>> PageAddItem with 16% of samples.
>
> Excellent.
>
> I'm slightly worried though since that seems to have changed from 8.2,
> which I oprofiled over Christmas. I can't recall what's changed though.
> Was this just on one system? Is it possible there is an effect on one
> system and not another?

Well, there's one big change: your patch to suppress WAL logging on
tables created in the same transaction. I ran the test again, this time
creating the table in a separate transaction:

samples % image name app name
symbol name
5480 17.0366 postgres postgres
XLogInsert
3684 11.4531 postgres postgres
PageAddItem
3580 11.1298 libc-2.3.6.so postgres memcpy
2498 7.7660 postgres postgres DoCopy
1265 3.9327 postgres postgres
LWLockAcquire
1210 3.7617 postgres postgres
CopyReadLine
1042 3.2394 postgres postgres
LWLockRelease
1038 3.2270 postgres postgres
heap_formtuple
1033 3.2115 libc-2.3.6.so postgres
____strtol_l_internal
875 2.7203 postgres postgres hash_any

The profile will probably look somewhat different depending on your
data, encoding etc.

All the page locking related functions account for ~10% in total,
including the LWLockAcquire/Release, Pin/UnBuffer, hash_any and so on.
And then there's all the memcpying...

--
Heikki Linnakangas
EnterpriseDB http://www.enterprisedb.com