Re: [PATCHES] A couple of patches for PostgreSQL 64bit support
Koichi Suzuki [EMAIL PROTECTED] writes: Here're a couple of patches for PostgreSQL 64bit support. There're just two extension to 64bit, size of shared memory and transaction ID. I've applied the part of this that seemed reasonably noncontroversial, namely the fixes to do shared memory size calculation in size_t arithmetic instead of int arithmetic. (While at it, I extended the Size convention to all the shared memory sizing routines, not just buffers, and added code to detect overflows in the calculations. That way we don't need a 64 bit configure switch.) While I still remain unconvinced that there's any real-world need for more than 2Gb of shared_buffers, this change certainly makes the code more robust against configuration errors, and it has essentially zero cost (except maybe a few more milliseconds during postmaster start). On the other hand, I think the 64-bit XID idea needs considerably more work before being proposed again. That would incur serious costs due to the expansion of tuple headers, and there's no evidence that the distributed cost would be bought back by avoiding one vacuum pass every billion transactions. (Your description of the patch claimed that vacuuming requires shutting down the database, which is simply wrong.) Also, as previously noted, you can't just whack the size of XID around without considering side-effects on CID, OID, Datum, etc. regards, tom lane ---(end of broadcast)--- TIP 6: explain analyze is your friend
Re: [PATCHES] A couple of patches for PostgreSQL 64bit support
Mark, I've not seen CVS in detail. I begain this work against 8.0.1 and continued thru 8.0.2 to 8.0.3. It was not a great work. The patch is rather straightforward and I appreciate if you try to port against CVS. Mark Wong wrote: Hi, I grabbed the patches to try, but I was wondering if it would be more interesting to try them against CVS rather than 8.0.3 (and if it would be easy to port :)? Mark -- --- Koichi Suzuki Open Source Engineeering Departmeent, NTT DATA Intellilink Corporation Phone: +81-3-5566-9628 WWW: http://www.intellilink.co.jp -- ---(end of broadcast)--- TIP 5: don't forget to increase your free space map settings
Re: [PATCHES] A couple of patches for PostgreSQL 64bit support
I asked originally for some experimental evidence showing any value in having more than 2Gb of shared buffers. In the absence of any convincing demonstration, I'm not very inclined to worry about whether we can handle wider-than-int shared memory size. Hi, Attached is a result of pgbench with 64bit patch PostgreSQL (base is 8.0.1). Benchmark machine is dual opteron (1.4GHz, 1MB cache each) with 8GB of memory and 120GB of IDE hard disk. Koichi Suzuki wrote: I have some experimeltal data about this extension. I will gather it and post hopefully this weekend. --- Koichi Suzuki Open Source Engineeering Departmeent, NTT DATA Intellilink Corporation Phone: +81-3-5566-9628 WWW: http://www.intellilink.co.jp -- 64-bit-pgbench20050712.pdf Description: Adobe PDF document ---(end of broadcast)--- TIP 3: Have you checked our extensive FAQ? http://www.postgresql.org/docs/faq
Re: [PATCHES] A couple of patches for PostgreSQL 64bit support
Hi, Attached is a result of pgbench with 64bit patch PostgreSQL (base is 8.0.1). Benchmark machine is dual opteron (1.4GHz, 1MB cache each) with 8GB of memory and 120GB of IDE hard disk. Koichi Suzuki wrote: I have some experimeltal data about this extension. I will gather it and post hopefully this weekend. -- --- Koichi Suzuki Open Source Engineeering Departmeent, NTT DATA Intellilink Corporation Phone: +81-3-5566-9628 WWW: http://www.intellilink.co.jp -- 64-bit-pgbench20050712.pdf Description: Adobe PDF document ---(end of broadcast)--- TIP 1: if posting/reading through Usenet, please send an appropriate subscribe-nomail command to [EMAIL PROTECTED] so that your message can get through to the mailing list cleanly
Re: [PATCHES] A couple of patches for PostgreSQL 64bit support
Koichi Suzuki [EMAIL PROTECTED] writes: Here're a couple of patches for PostgreSQL 64bit support. There're just two extension to 64bit, size of shared memory and transaction ID. I asked originally for some experimental evidence showing any value in having more than 2Gb of shared buffers. In the absence of any convincing demonstration, I'm not very inclined to worry about whether we can handle wider-than-int shared memory size. As for the XID change, I don't think this patch accurately reflects the size of the impact. There are a lot of things that in practice need to be the same size as XID (CID, most obviously, but I suspect also OID). And again, some demonstration of the performance impact would be appropriate. Here, not only do you have to prove that widening XID isn't a big performance hit in itself, but you also have to convince us that it's a win compared to the existing approach of vacuuming at least every billion transactions. regards, tom lane ---(end of broadcast)--- TIP 6: Have you searched our list archives? http://archives.postgresql.org
Re: [PATCHES] A couple of patches for PostgreSQL 64bit support
Tom Lane wrote: Koichi Suzuki [EMAIL PROTECTED] writes: Here're a couple of patches for PostgreSQL 64bit support. There're just two extension to 64bit, size of shared memory and transaction ID. I asked originally for some experimental evidence showing any value in having more than 2Gb of shared buffers. In the absence of any convincing demonstration, I'm not very inclined to worry about whether we can handle wider-than-int shared memory size. There is some practical evidence. Recently the number of large boxes in the field is almost growing exponentially. Today I have heard somebody say this box has 'just 4 gig of ram' . On large installations we have already seen problems with too small caches (= 2gb). Surprisingly this has turned out to be a quite important issue in the field. Tests have shown that the cache provided by the OS is a lot worse for the database. 64-bit XIDs seem to be an overkill - the only practical impact I can see is an even larger tuple header (this can be an issue on large boxes too - at least compared to Oracle). Best regards, Hans ---(end of broadcast)--- TIP 3: if posting/reading through Usenet, please send an appropriate subscribe-nomail command to [EMAIL PROTECTED] so that your message can get through to the mailing list cleanly
Re: [PATCHES] A couple of patches for PostgreSQL 64bit support
=?ISO-8859-1?Q?Hans-J=FCrgen_Sch=F6nig?= [EMAIL PROTECTED] writes: There is some practical evidence. Recently the number of large boxes in the field is almost growing exponentially. Today I have heard somebody say this box has 'just 4 gig of ram' . On large installations we have already seen problems with too small caches (= 2gb). Surprisingly this has turned out to be a quite important issue in the field. Tests have shown that the cache provided by the OS is a lot worse for the database. *What* tests? This is all handwaving :-( What I would find credible is a set of, say, OSDL test runs, showing a continuing increase of performance with shared_buffers right up to the 2Gb limit. Everything done to date says that you hit the point of diminishing returns well before that. regards, tom lane ---(end of broadcast)--- TIP 7: don't forget to increase your free space map settings
Re: [PATCHES] A couple of patches for PostgreSQL 64bit support
Tom Lane wrote: =?ISO-8859-1?Q?Hans-J=FCrgen_Sch=F6nig?= [EMAIL PROTECTED] writes: There is some practical evidence. Recently the number of large boxes in the field is almost growing exponentially. Today I have heard somebody say this box has 'just 4 gig of ram' . On large installations we have already seen problems with too small caches (= 2gb). Surprisingly this has turned out to be a quite important issue in the field. Tests have shown that the cache provided by the OS is a lot worse for the database. *What* tests? This is all handwaving :-( What I would find credible is a set of, say, OSDL test runs, showing a continuing increase of performance with shared_buffers right up to the 2Gb limit. Everything done to date says that you hit the point of diminishing returns well before that. regards, tom lane well, you can easily try it on a big machine with gigs of ram and nothing but the database running. using a very low number of shared buffers will lead to worse performance than many shared buffers - even if the operating system caches some disk i/O (which is done by linux if nobody else want to have some ram). i have no public hard figures i could post here but customers have told me that 2Q cache vs. kernel cache is around 5-10 times faster (it varies of course). the 2gb thing is especially important for data crunchers - not necessarily for 'normal' OLTP databases. just assume somebody getting 5 gig of data and doing some repeated computation with this data. you definitely don't want to go to disk in this case. people will assume that postgresql can work with large caches (it is a good database - why do i get errors on startup - this is the usual story). people rather tend to rely on PostgreSQL than on some operating system thing ;). i might have some time to provide some real hard facts to prove this but i am a bit busy at the moment. best regards, hans ---(end of broadcast)--- TIP 3: if posting/reading through Usenet, please send an appropriate subscribe-nomail command to [EMAIL PROTECTED] so that your message can get through to the mailing list cleanly
Re: [PATCHES] A couple of patches for PostgreSQL 64bit support
I have some experimeltal data about this extension. I will gather it and post hopefully this weekend. Tom Lane wrote: Koichi Suzuki [EMAIL PROTECTED] writes: Here're a couple of patches for PostgreSQL 64bit support. There're just two extension to 64bit, size of shared memory and transaction ID. I asked originally for some experimental evidence showing any value in having more than 2Gb of shared buffers. In the absence of any convincing demonstration, I'm not very inclined to worry about whether we can handle wider-than-int shared memory size. As for the XID change, I don't think this patch accurately reflects the size of the impact. There are a lot of things that in practice need to be the same size as XID (CID, most obviously, but I suspect also OID). And again, some demonstration of the performance impact would be appropriate. Here, not only do you have to prove that widening XID isn't a big performance hit in itself, but you also have to convince us that it's a win compared to the existing approach of vacuuming at least every billion transactions. regards, tom lane -- --- Koichi Suzuki Open Source Engineeering Departmeent, NTT DATA Intellilink Corporation Phone: +81-3-5566-9628 WWW: http://www.intellilink.co.jp -- ---(end of broadcast)--- TIP 5: Have you checked our extensive FAQ? http://www.postgresql.org/docs/faq
Re: [PATCHES] A couple of patches for PostgreSQL 64bit support
Hans-J|rgen Schvnig [EMAIL PROTECTED] wrote: 64-bit XIDs seem to be an overkill - the only practical impact I can see is an even larger tuple header (this can be an issue on large boxes too - at least compared to Oracle). I agreed, too. The changes of XIDs cannot be ignored because the overhead will be 32bytes per tuple. Avoiding overheads, can XIDs/CIDs be different bit length? For example, can XIDs/CIDs be changed to 48/16-bit or 40/24-bit? --- ITAGAKI Takahiro NTT Cyber Space Laboratories ---(end of broadcast)--- TIP 8: explain analyze is your friend
