Re: Reduce heap tuple header size
От | Bruce Momjian |
---|---|
Тема | Re: Reduce heap tuple header size |
Дата | |
Msg-id | 200206251338.g5PDcqk06205@candle.pha.pa.us обсуждение исходный текст |
Ответ на | Re: Reduce heap tuple header size (Jan Wieck <JanWieck@Yahoo.com>) |
Список | pgsql-patches |
Jan, any update on this? Are the numbers correct? --------------------------------------------------------------------------- Jan Wieck wrote: > Bruce Momjian wrote: > > > > Jan Wieck wrote: > > > > > > Did someone run at least pgbench with/without that patch applied? > > > > No, but he did perform this analysis: > > > > > thus reducing the additional cost to one t_infomask compare, > > > because the Satisfies functions only access Cmin and Cmax, > > > when HEAP_MOVED is known to be not set. > > > > > > OTOH experimenting with a moderatly sized "out of production" > > > database I got the following results: > > > | pages | pages | > > > relkind | count | tuples | before| after | savings > > > --------+-------+--------+-------+-------+-------- > > > i | 31 | 808146 | 8330 | 8330 | 0.00% > > > r | 32 | 612968 | 13572 | 13184 | 2.86% > > > all | 63 | | 21902 | 21514 | 1.77% > > > > > > 2.86% fewer heap pages mean 2.86% less disk IO caused by heap pages. > > > Considering that index pages tend to benefit more from caching > > > we conclude that heap pages contribute more to the overall > > > IO load, so the total savings in the number of disk IOs should > > > be better than the 1.77% shown in the table above. I think > > > this outweighs a few CPU cycles now and then. > > This anawhat? This is a proof that this patch is able to save not even > 3% of disk space in a production environment plus an assumption that the > saved IO outweights the extra effort in the tuple visibility checks. > > Here are some numbers: > > P3 850MHz 256MB RAM IDE > postmaster -N256 -B8192 > pgbench -i -s 10 db > pgbench -c 20 -t 500 db > > > Current CVS tip: tps 34.1, 38.7, 36.6 > avg(tps) 36.4 > > With patch: tps 37.0, 41.1, 41.1 > avg(tps) 39.7 > > So it saves less than 3% disk space at the cost of about 9% performance > loss. If we can do the same the other way around I'd go for wasting some > more disk space. > > > Jan > > -- > > #======================================================================# > # It's easier to get forgiveness for being wrong than for being right. # > # Let's break this rule - forgive me. # > #================================================== JanWieck@Yahoo.com # > > ---------------------------(end of broadcast)--------------------------- > TIP 1: subscribe and unsubscribe commands go to majordomo@postgresql.org > -- Bruce Momjian | http://candle.pha.pa.us pgman@candle.pha.pa.us | (610) 853-3000 + If your life is a hard drive, | 830 Blythe Avenue + Christ can be your backup. | Drexel Hill, Pennsylvania 19026
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