gt; > Subject: Re: [HACKERS] qsort again (was Re: [PERFORM] Strange Create
> Index
> > behaviour)
> >
> > Ron <[EMAIL PROTECTED]> writes:
> > > How are we choosing our pivots?
> >
> > See qsort.c: it looks like median of nine equally spaced input
> -Original Message-
> From: [EMAIL PROTECTED] [mailto:pgsql-hackers-
> [EMAIL PROTECTED] On Behalf Of Markus Schaber
> Sent: Thursday, February 16, 2006 5:45 AM
> To: pgsql-performance@postgresql.org; pgsql-hackers@postgresql.org
> Subject: Re: [HACKERS] qsort again
Last night I implemented a non-recursive introsort in C... let me test it a bit more and then I'll post it here for everyone else to try out.On 2/16/06, Markus Schaber
<[EMAIL PROTECTED]> wrote:Hi, Ron,
Ron wrote:> ...and of course if you know enough about the data to be sorted so as to> constrain
> -Original Message-
> From: [EMAIL PROTECTED] [mailto:pgsql-hackers-
> [EMAIL PROTECTED] On Behalf Of Tom Lane
> Sent: Wednesday, February 15, 2006 5:22 PM
> To: Ron
> Cc: pgsql-performance@postgresql.org; pgsql-hackers@postgresql.org
> Subject: Re: [HACKERS
Mark Lewis <[EMAIL PROTECTED]> writes:
> I think we're actually on the same page here; you're right that the
> constraint above ( f(a)==f(b) iff a==b ) can't be extended to data types
> with more than 32 bits of value space. But the constraint I listed was
> actually:
> if a==b then f(a)==f(b)
I
On Thu, 2006-02-16 at 21:33 -0800, David Lang wrote:
> > In SQL_ASCII, just take the first 4 characters (or 8, if using a 64-bit
> > sortKey as elsewhere suggested). The sorting key doesn't need to be a
> > one-to-one mapping.
>
> that would violate your second contraint ( f(a)==f(b) iff (a==b) )
On Fri, Feb 17, 2006 at 08:18:41AM -0800, Scott Lamb wrote:
> On Feb 16, 2006, at 2:17 PM, Mark Lewis wrote:
> >Data types which could probably provide a useful function for f
> >would be
> >int2, int4, oid, and possibly int8 and text (at least for SQL_ASCII).
>
> ...and with some work, floats (
On Feb 16, 2006, at 2:17 PM, Mark Lewis wrote:Data types which could probably provide a useful function for f would be int2, int4, oid, and possibly int8 and text (at least for SQL_ASCII). ...and with some work, floats (I think just the exponent would work, if nothing else). bytea. Probably just ab
Hi, David,
David Lang schrieb:
>> In SQL_ASCII, just take the first 4 characters (or 8, if using a 64-bit
>> sortKey as elsewhere suggested). The sorting key doesn't need to be a
>> one-to-one mapping.
> that would violate your second contraint ( f(a)==f(b) iff (a==b) )
no, it doesn't.
When b
On Thu, 16 Feb 2006, Mark Lewis wrote:
On Thu, 2006-02-16 at 17:51 -0500, Greg Stark wrote:
Data types which could probably provide a useful function for f would be
int2, int4, oid, and possibly int8 and text (at least for SQL_ASCII).
How exactly do you imagine doing this for text?
I could s
On Fri, Feb 17, 2006 at 12:05:23AM +0100, PFC wrote:
> I would have said a 64 bit int, but it's the same idea. However it
> won't work for floats, which is a pity, because floats fit in 64 bits.
Actually, you can compare IEEE floats directly as ints, as long as they're
positive. (If
Hi, PFC,
PFC schrieb:
> By the way, I'd like to declare my zipcode columns as SQL_ASCII
> while the rest of my database is in UNICODE, so they are faster to
> index and sort. Come on, MySQL does it...
Another use case for parametric column definitions - charset definitions
- and the first
On Thu, 2006-02-16 at 17:51 -0500, Greg Stark wrote:
> > > Data types which could probably provide a useful function for f would be
> > > int2, int4, oid, and possibly int8 and text (at least for SQL_ASCII).
>
> How exactly do you imagine doing this for text?
>
> I could see doing it for char(n)/
It seems that instead of maintaining a different sorting code path for
each data type, you could get away with one generic path and one
(hopefully faster) path if you allowed data types to optionally support
a 'sortKey' interface by providing a function f which maps inputs to 32-
bit int output
Markus Schaber <[EMAIL PROTECTED]> writes:
> Hmm, to remove redundancy, I'd change the <= to a < and define:
>
> if a==b then f(a)==f(b)
> if a
> > Data types which could probably provide a useful function for f would be
> > int2, int4, oid, and possibly int8 and text (at least for SQL_ASCII).
On Thu, Feb 16, 2006 at 02:17:36PM -0800, Mark Lewis wrote:
> It seems that instead of maintaining a different sorting code path for
> each data type, you could get away with one generic path and one
> (hopefully faster) path if you allowed data types to optionally support
> a 'sortKey' interface b
Hi, Mark,
Mark Lewis schrieb:
> It seems that instead of maintaining a different sorting code path for
> each data type, you could get away with one generic path and one
> (hopefully faster) path if you allowed data types to optionally support
> a 'sortKey' interface by providing a function f whi
On Thu, 2006-02-16 at 12:15 -0500, Tom Lane wrote:
> Once or twice we've kicked around the idea of having some
> datatype-specific sorting code paths alongside the general-purpose one,
> but I can't honestly see this as being workable from a code maintenance
> standpoint.
>
>
"Gary Doades" <[EMAIL PROTECTED]> writes:
> I think the reason I wasn't seeing performance issues with normal sort
> operations is because they use work_mem not maintenance_work_mem which was
> only set to 2048 anyway. Does that sound right?
Very probable. Do you want to test the theory by jackin
"Craig A. James" <[EMAIL PROTECTED]> writes:
> You can also use this trick when the optimizer is asked for "fastest first
> result." Say you have a cursor on a column of numbers with good
> distribution. If you do a bucket sort on the first two or three digits only,
> you know the first "page"
> "Gary Doades" <[EMAIL PROTECTED]> writes:
>> I think the reason I wasn't seeing performance issues with normal sort
>> operations is because they use work_mem not maintenance_work_mem which
>> was
>> only set to 2048 anyway. Does that sound right?
>
> Very probable. Do you want to test the theor
On Thu, Feb 16, 2006 at 08:22:55AM -0500, Ron wrote:
> 3= Especially in modern systems where the gap between internal CPU
> bandwidth and memory bandwidth is so great, the overhead of memory
> accesses for comparisons and moves is the majority of the overhead
> for both the pivot choosing and th
Tom Lane wrote:
> I increased the size of the test case by 10x (basically s/10/100/)
> which is enough to push it into the external-sort regime. I get
> amazingly stable runtimes now --- I didn't have the patience to run 100
> trials, but in 30 trials I have slowest 11538 msec and fastest
On Wed, 2006-02-15 at 18:28 -0500, Tom Lane wrote:
> It seems clear that our qsort.c is doing a pretty awful job of picking
> qsort pivots, while glibc is mostly managing not to make that mistake.
> I haven't looked at the glibc code yet to see what they are doing
> differently.
glibc qsort is act
On Wed, 2006-02-15 at 19:59 -0500, Tom Lane wrote:
> I get
> amazingly stable runtimes now --- I didn't have the patience to run 100
> trials, but in 30 trials I have slowest 11538 msec and fastest 11144 msec.
> So this code path is definitely not very sensitive to this data
> distribution.
"The
I wrote:
> Gary Doades <[EMAIL PROTECTED]> writes:
>> Ouch! That confirms my problem. I generated the random test case because
>> it was easier than including the dump of my tables, but you can
>> appreciate that tables 20 times the size are basically crippled when it
>> comes to creating an ind
Gary Doades <[EMAIL PROTECTED]> writes:
> Ouch! That confirms my problem. I generated the random test case because
> it was easier than including the dump of my tables, but you can
> appreciate that tables 20 times the size are basically crippled when it
> comes to creating an index on them.
Ac
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