Re: [HACKERS] Polyphase merge is obsolete

2017-09-11 Thread Tomas Vondra
Hi, I planned to do some benchmarking on this patch, but apparently the patch no longer applies. Rebase please? regards -- Tomas Vondra http://www.2ndQuadrant.com PostgreSQL Development, 24x7 Support, Remote DBA, Training & Services -- Sent via pgsql-hackers mailing list

Re: [HACKERS] Polyphase merge is obsolete

2017-08-30 Thread Peter Geoghegan
On Wed, Aug 30, 2017 at 12:48 PM, Robert Haas wrote: > These are separate topics. They should each be discussed on their own > thread. Please don't hijack this thread to talk about something else. I don't think that that is a fair summary. Heikki has done a number of

Re: [HACKERS] Polyphase merge is obsolete

2017-08-30 Thread Robert Haas
On Wed, Aug 30, 2017 at 2:54 PM, Peter Geoghegan wrote: > I noticed that this is in the upcoming CF 1 for v11. I'm signed up to review. > > I'd like to point out that replacement selection is also obsolete, > which is something I brought up recently [1]. I don't actually have > any

Re: [HACKERS] Polyphase merge is obsolete

2017-08-30 Thread Peter Geoghegan
On Mon, Feb 27, 2017 at 2:45 PM, Peter Geoghegan wrote: > Since we have an awful lot of stuff in the last CF, and this patch > doesn't seem particularly strategic, I've marked it "Returned with > Feedback". I noticed that this is in the upcoming CF 1 for v11. I'm signed up to

Re: [HACKERS] Polyphase merge is obsolete

2017-02-27 Thread Peter Geoghegan
On Mon, Jan 16, 2017 at 5:56 PM, Peter Geoghegan wrote: > On Wed, Oct 12, 2016 at 10:16 AM, Heikki Linnakangas wrote: >> The number of *input* tapes we can use in each merge pass is still limited, >> by the memory needed for the tape buffers and the merge heap,

Re: [HACKERS] Polyphase merge is obsolete

2017-01-16 Thread Peter Geoghegan
On Wed, Oct 12, 2016 at 10:16 AM, Heikki Linnakangas wrote: > The number of *input* tapes we can use in each merge pass is still limited, > by the memory needed for the tape buffers and the merge heap, but only one > output tape is active at any time. The inactive output tapes

Re: [HACKERS] Polyphase merge is obsolete

2016-10-14 Thread Peter Geoghegan
On Wed, Oct 12, 2016 at 10:16 AM, Heikki Linnakangas wrote: > Let's switch over to a simple k-way balanced merge. Because it's simpler. If > you're severely limited on memory, like when sorting 1GB of data with > work_mem='1MB' or less, it's also slightly faster. I'm not too

Re: [HACKERS] Polyphase merge is obsolete

2016-10-12 Thread Heikki Linnakangas
On 10/12/2016 08:27 PM, Tom Lane wrote: Heikki Linnakangas writes: The beauty of the polyphase merge algorithm is that it allows reusing input tapes as output tapes efficiently ... So the whole idea of trying to efficiently reuse input tapes as output tapes is pointless.

Re: [HACKERS] Polyphase merge is obsolete

2016-10-12 Thread Tom Lane
Heikki Linnakangas writes: > The beauty of the polyphase merge algorithm is that it allows reusing > input tapes as output tapes efficiently ... So the whole idea of trying to > efficiently reuse input tapes as output tapes is pointless. It's been awhile since I looked at that

[HACKERS] Polyphase merge is obsolete

2016-10-12 Thread Heikki Linnakangas
The beauty of the polyphase merge algorithm is that it allows reusing input tapes as output tapes efficiently. So if you have N tape drives, you can keep them all busy throughout the merge. That doesn't matter, when we can easily have as many "tape drives" as we want. In PostgreSQL, a tape