On Tue, 26 Jan 2010, Saulius Zrelskis wrote: Hi,
> I want to share my observations how differs > Clipper and Harbour IO activity on exclusive opened dbf file. > Clipper 5.2 and 5.3 module dbf1.c, function dbfRead on shared > database reads only selected record with _fsRead, > but for exclusive database reads in 1024 bytes chunks > as many records, as possible with _xpage_read. > The same with writing: shared with _fsWrite and exclusive > with _xpage_update. Yes. Clipper seems to use the same caches with 1024 bytes page size for indexes and exclusive mode DBF tables. > Harbour reads and writes records one-by-one not depending on > access mode. Harbour does not use any caches so far with the exception to index tree paths but it's only few pages so it can be ignored. > Prepared simple wrappers to Clipper low-level APIs _fs*, > and Harbour APIs hb_fs* from module filesys.c registers > calls to these APIs. [...] > From logs we can see, that Clipper uses for this sample > 12 calls (4 read and 8 write). > Harbour uses 302 calls (102 read and 180 write)! > Log file attached. > > Clipper uses buffering data on IO requests. > Buffering can speed up IO quite a bit. > Rather than reading one record at a time from the network or disk, > Clipper reads a larger block at a time. This is typically much faster, > big amount of IO requests detrimental to performance in network > environment. > Is there plans to introduce buffered IO for dbf files? In current RDD code all IO API is redirected to replaceable IO functions so anyone can write such caching system for all core RDDs without touching their code. It's enough to write simple HB_FILE IO driver like NETIO or MEMIO. I can try to write it in some spare time but maybe someone else can do it too. As I can see you wrote some wrappers to Clipper functions so I guess you have enough knowledge to create new HB_FILE IO driver adding buffering for all files open in exclusive mode with name starting with "buf:". What do you think about it? best regards, Przemek _______________________________________________ Harbour mailing list (attachment size limit: 40KB) Harbour@harbour-project.org http://lists.harbour-project.org/mailman/listinfo/harbour
