Menu
▾
▴
Re: [Pytables-users] searching for group names
|
From: Gabriel J.L. B. <pyt...@gb...> - 2013-08-07 11:39:31
|
Hi, I don't know if this is related in any way to Gergo's problem, but I have slow responses when querying which children a group contains, if that group contains big leafs. I am using pytables 2.5 and hdf5 1.8.9 on linux 64 bit. Specifically, I found that using the _g_get_objinfo method (which is used by other methods that I use) is slow when used on a large leaf. The slowness is proportional to the size of the leaf. It is almost as if some process is actually reading the data instead of just info on the type of data. I am noticing this because my data is on an external usb3 disk. To give you an idea: that method takes almost 80 seconds to return the string 'Leaf' when used on a 5 Gb EArray. That should roughly correspond to reading the complete disk-based array. The info is cached somehow, because if I run the method a second time in the same python session it is very fast. If I copy my hdf5 file to my SSD disk, things are much faster, but running the method still takes 2 seconds or so on a 5 Gb leaf. Is this expected behavior and should I just avoid this method in my applications, or is something wrong? Best, Gabriel Anthony Scopatz <sc...@gm...> schreef: > On Mon, Aug 5, 2013 at 4:11 AM, Nyirő Gergő <ger...@gm...> wrote: > >> Hello, >> >> >> We develop a measurement evaluation tool, and we'd like to use >> pytables/hdf5 as a middle layer for signal accessing. >> >> We have to deal with the silly structure of the recorder device >> measurement format. >> >> >> >> The signals can be accessed via two identifiers: >> >> * device name: <source of the signal>-<channel of the >> message>-<another tag>-<yet another tag> >> >> * signal name >> >> >> >> The first identifier says the source information of the signal, which >> can be quite long. >> >> Therefore I grouped the device name into two layers: >> >> /<source of the signal> >> >> /<channel of the message>... >> >> /<signal name> >> >> >> >> So if you have the same message from two channels, than you will get >> /foo-device-name >> >> /channel-1 >> >> /bar >> >> /baz >> >> /channel-2 >> >> /bar >> >> /baz >> >> >> >> Besides signal loading, we have to search for signal name as fast as >> possible, and return with the shortest unique device name part and the >> signal name. >> >> Using the structure above, iterating over the group names is quite >> slow. So I build up a table from device and signal name. >> >> As far as I know, the pytables query does not support string searching >> (e.g. startswidth, *foo[0-9]ch*, etc.), so fetching this table lead us >> to a pure python loop which is slow again. >> >> Therefore I build up a python dictionary from the table, which provide >> fast iteration against the table, but the init time increased from 100 >> ms to 3-4 sec (we have more than 40 000 signals). >> >> >> >> Do you have any advice how to search for group names in hdf5 with >> pytables in an efficient way? >> > > Hi grego, > > Searching through group names, like accessing all HDF5 metadata, is slow. > For group names this is because rather than searching through a list you > are traversing a B-tree, IIRC. So you have to use the couple of tricks > that you used: 1) have another Table / Array of all table names, 2) read > this in once to a native Python data structure (dict here). > > However, 4 sec to read in this table seems excessive for data of this size. > You are probably not reading this in properly. You should be using: > > raw_grps = f.root.grp_names[:] > > or similar. > > Maybe other people have some other ideas. > > Be Well > Anthony > > >> >> ps: I would be most happy with a glob interface. >> >> >> >> thanks for your advices in advance, >> >> gergo >> >> >> ------------------------------------------------------------------------------ >> Get your SQL database under version control now! >> Version control is standard for application code, but databases havent >> caught up. So what steps can you take to put your SQL databases under >> version control? Why should you start doing it? Read more to find out. >> http://pubads.g.doubleclick.net/gampad/clk?id=49501711&iu=/4140/ostg.clktrk >> _______________________________________________ >> Pytables-users mailing list >> Pyt...@li... >> https://lists.sourceforge.net/lists/listinfo/pytables-users >> |