Neil Conway wrote: > toast_compress_datum() considers compression to be "successful" if the > compressed version of the datum is smaller than the uncompressed > version. I think this is overly generous: if compression reduces the > size of the datum by, say, 0.01%, it is likely a net loss to use the > compressed version of the datum since we'll need to pay for LZ > decompression every time that we de-TOAST it. This situation can occur > frequently when storing "mostly-uncompressible" data (compressed images, > encrypted data, etc.) -- some parts of the data will compress well (e.g. > metadata), but the vast majority will not. > > It's true that LZ decompression is fast, so we should probably use the > compressed version of the datum unless the reduction in size is very > small. I'm not sure precisely what that threshold should be, however. > > Comments?
20%? 25% -- Bruce Momjian http://candle.pha.pa.us SRA OSS, Inc. http://www.sraoss.com + If your life is a hard drive, Christ can be your backup. + ---------------------------(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
