Il 07/08/2018 19:41, Abroży Nieprzełoży ha scritto: > substr(data, start, len) loads entire value and then substrs it. > sqlite3_blob_read reads the desired parts.
I've verified that not only substr(data, start, len) loads entire row, but with my surprise that also retrieving a sibling column (I've tried to add another column "info blob not null") loads entire row (i.e. including whole data column)... IOW "select info from content;" retrieves also data column content. Weird, isn't it? > > 2018-08-06 20:59 GMT+02:00, Abramo Bagnara <abramo.bagn...@bugseng.com>: >> Il 04/08/2018 07:07, Abramo Bagnara ha scritto: >>> Il 03/08/2018 23:53, Abroży Nieprzełoży ha scritto: >>>> -- One table with whole files >>>> CREATE TABLE content( >>>> id INTEGER PRIMARY KEY, >>>> data BLOB NOT NULL >>>> ); >>>> -- And second table with line boundaries >>>> CREATE TABLE lines( >>>> id INTEGER NOT NULL REFERENCES content(id), >>>> line_no INTEGER NOT NULL, >>>> bytes_from INTEGER NOT NULL, >>>> bytes_to INTEGER NOT NULL, >>>> PRIMARY KEY(id, line_num) >>>> ) WITHOUT ROWID; >>>> -- Use Incremental BLOB I/O https://www.sqlite.org/c3ref/blob_open.html >>> >>> Incremental BLOB I/O is faster than using substr(data, start, len) in a >>> SELECT? >> >> Someone familiar with implementation of BLOB I/O and sqlite VM can >> answer to that? >> >> I'd guess that *if* there is a difference it is greater with bigger >> blobs, but it is also possible there is not any sensible difference if >> substr act similarly to sqlite3_blob_read. >> >> But my uninformed guesses are definitely not relevant, until an aware >> Samaritan will come to clarify that ;-) >> -- Abramo Bagnara BUGSENG srl - http://bugseng.com mailto:abramo.bagn...@bugseng.com _______________________________________________ sqlite-users mailing list sqlite-users@mailinglists.sqlite.org http://mailinglists.sqlite.org/cgi-bin/mailman/listinfo/sqlite-users
