Richard, Paul thanks! You help me so much. Omitting WITHOUT ROWID do the trick.
2014-12-02 3:04 GMT+07:00 Paul Sanderson <sandersonforens...@gmail.com>: > Further to Richards comment the formula to determine when a record > overflows into a page file is given in section 1.5 of the file format > doc > > http://www.sqlite.org/fileformat.html > > The relevant section states: > > The amount of payload that spills onto overflow pages also depends on > the page type. For the following computations, let U be the usable > size of a database page, the total page size less the reserved space > at the end of each page. And let P be the payload size. > > Table B-Tree Leaf Cell: > > If the payload size P is less than or equal to U-35 then the entire > payload is stored on the b-tree leaf page. Let M be > ((U-12)*32/255)-23. If P is greater than U-35 then the number of byte > stored on the b-tree leaf page is the smaller of M+((P-M)%(U-4)) and > U-35. Note that number of bytes stored on the leaf page is never less > than M. > > So in your case with a max blob size of 49870 bytes (which is > U-35) > so as far as I see it all the blobs can fit onto a single page and > acccording to that formula they should be. > > Certainly in my testing I used your schema (with rowids) and wrote a > single blob of size 60000 bytes to a DB with a pagesize of 65536 bytes > and the complete blob was stored in one page as expected (and as shown > below). > > http://sandersonforensics.com/pics/largeblobhdr.jpg > > http://sandersonforensics.com/pics/largeblob.jpg > > You have truncated some of the data for DBs with page size > 512 - I > assume you have determined that this is not relevant but without the > info I can't draw any conclusions. I also assume that you started a > new instance of sqlite between tests? > > Perhaps I could suggest that you do a similar test to mine just adding > one (or a small handful) of blobs to the table and see if this sheds > any light on what is going on. > > > > > > > > > Paul > www.sandersonforensics.com > skype: r3scue193 > twitter: @sandersonforens > Tel +44 (0)1326 572786 > http://sandersonforensics.com/forum/content.php?195-SQLite-Forensic-Toolkit > -Forensic Toolkit for SQLite > http://sandersonforensics.com/forum/content.php?168-Reconnoitre - VSC > processing made easy > > > > On 1 December 2014 at 13:13, Richard Hipp <d...@sqlite.org> wrote: > > On Sun, Nov 30, 2014 at 11:06 PM, Александр Гурьянов < > caiiiy...@gmail.com> > > wrote: > > > >> Hi. Hi. I am writing an app that stores some blobs in sqlite3 database. > My > >> question is about disk space usage. > >> For analyst i use sqlite_analyzer. > >> > >> My database is created with this script: > >> > >> PRAGMA page_size = 512; > >> PRAGMA synchronous = OFF; > >> PRAGMA journal_mode = MEMORY; > >> begin; > >> create table grid_blobs(grid_id integer, blob blob, PRIMARY > KEY(grid_id)) > >> WITHOUT ROWID; > >> > > > > You'll have much better success here if you omit the WITHOUT ROWID. See > > section 4.0 "When to use WITHOUT ROWID" at > > https://www.sqlite.org/withoutrowid.html for additional information. > > > > See also: http://www.sqlite.org/affcase1.html#smaller > > > > > > > > > >> insert into grid_blobs values(0, randomblob(70)); > >> insert into grid_blobs values(1, randomblob(66)); > >> insert into grid_blobs values(2, randomblob(82)); > >> insert into grid_blobs values(3, randomblob(79)); > >> insert into grid_blobs values(4, randomblob(67)); > >> insert into grid_blobs values(5, randomblob(124)); > >> insert into grid_blobs values(6, randomblob(119)); > >> insert into grid_blobs values(7, randomblob(70)); > >> insert into grid_blobs values(8, randomblob(82)); > >> insert into grid_blobs values(9, randomblob(75)); > >> --... (other entries) > >> insert into grid_blobs values(2703, randomblob(698)); > >> commit; > >> > >> There are 2703 entries with blob length from 31 bytes up to 49870 bytes > >> (avg: 2297, median: 332). > >> The output of sqlite_analyzer for this table is: > >> > >> sqlite3 test.db "PRAGMA page_size=512; vacuum;" && > >> ~/Downloads/sqlite3_analyzer test.db > analyze > >> Percentage of total database...................... 99.984% > >> Number of entries................................. 2437 > >> Bytes of storage consumed......................... 3229184 > >> Bytes of payload.................................. 2608484 80.8% > >> Average payload per entry......................... 1070.37 > >> Average unused bytes per entry.................... 235.34 > >> Average fanout.................................... 8.00 > >> Non-sequential pages.............................. 0 0.0% > >> Maximum payload per entry......................... 49877 > >> Entries that use overflow......................... 2321 95.2% > >> Index pages used.................................. 35 > >> Primary pages used................................ 268 > >> Overflow pages used............................... 6004 > >> Total pages used.................................. 6307 > >> Unused bytes on index pages....................... 1774 9.9% > >> Unused bytes on primary pages..................... 8836 6.4% > >> Unused bytes on overflow pages.................... 562916 18.3% > >> Unused bytes on all pages......................... 573526 17.8% > >> > >> sqlite3 test.db "PRAGMA page_size=1024; vacuum;" && > >> ~/Downloads/sqlite3_analyzer test.db > analyze > >> Unused bytes on index pages....................... 4679 10.6% > >> Unused bytes on primary pages..................... 17233 5.7% > >> Unused bytes on overflow pages.................... 933114 28.7% > >> Unused bytes on all pages......................... 955026 26.5% > >> > >> sqlite3 test.db "PRAGMA page_size=2048; vacuum;" && > >> ~/Downloads/sqlite3_analyzer test.db > analyze > >> Unused bytes on index pages....................... 13738 14.6% > >> Unused bytes on primary pages..................... 37882 6.6% > >> Unused bytes on overflow pages.................... 1184110 37.0% > >> Unused bytes on all pages......................... 1235730 31.9% > >> > >> sqlite3 test.db "PRAGMA page_size=4096; vacuum;" && > >> ~/Downloads/sqlite3_analyzer test.db > analyze > >> Unused bytes on index pages....................... 16017 12.6% > >> Unused bytes on primary pages..................... 57645 6.3% > >> Unused bytes on overflow pages.................... 1264444 43.2% > >> Unused bytes on all pages......................... 1338106 33.7% > >> > >> sqlite3 test.db "PRAGMA page_size=8192; vacuum;" && > >> ~/Downloads/sqlite3_analyzer test.db > analyze > >> Unused bytes on index pages....................... 31248 18.2% > >> Unused bytes on primary pages..................... 70063 5.5% > >> Unused bytes on overflow pages.................... 1535111 54.6% > >> Unused bytes on all pages......................... 1636422 38.4% > >> > >> sqlite3 test.db "PRAGMA page_size=16384; vacuum;" && > >> ~/Downloads/sqlite3_analyzer test.db > analyze > >> Unused bytes on index pages....................... 52549 24.7% > >> Unused bytes on primary pages..................... 88974 5.1% > >> Unused bytes on overflow pages.................... 1202291 59.7% > >> Unused bytes on all pages......................... 1343814 33.9% > >> > >> sqlite3 test.db "PRAGMA page_size=32768; vacuum;" && > >> ~/Downloads/sqlite3_analyzer test.db > analyze > >> Unused bytes on index pages....................... 36957 18.8% > >> Unused bytes on primary pages..................... 104610 5.0% > >> Unused bytes on overflow pages.................... 1104895 70.2% > >> Unused bytes on all pages......................... 1246462 32.2% > >> > >> sqlite3 test.db "PRAGMA page_size=65536; vacuum;" && > >> ~/Downloads/sqlite3_analyzer test.db > analyze > >> Unused bytes on index pages....................... 115861 44.2% > >> Unused bytes on primary pages..................... 179123 7.2% > >> Unused bytes on overflow pages.................... 427834 72.5% > >> Unused bytes on all pages......................... 722818 21.6% > >> > >> As you can see there are initially 18% of unused space in overflow > pages. > >> As far as I understand it means that there are > >> some blobs that do not fit into primary pages and these blobs are > stored in > >> overflow pages. But with increasing page size the unused space on > overflow > >> pages are also growth. Even when the page size is greater then max blob > >> size (page_size = 65536, max blob = 49870) there are 72.5% of unused > bytes > >> on overflow pages. Why? > >> > >> _______________________________________________ > >> sqlite-users mailing list > >> sqlite-users@sqlite.org > >> http://sqlite.org:8080/cgi-bin/mailman/listinfo/sqlite-users > >> > >> > > > > > > -- > > D. Richard Hipp > > d...@sqlite.org > > _______________________________________________ > > sqlite-users mailing list > > sqlite-users@sqlite.org > > http://sqlite.org:8080/cgi-bin/mailman/listinfo/sqlite-users > _______________________________________________ > sqlite-users mailing list > sqlite-users@sqlite.org > http://sqlite.org:8080/cgi-bin/mailman/listinfo/sqlite-users > -- С уважением, Гурьянов Александр _______________________________________________ sqlite-users mailing list sqlite-users@sqlite.org http://sqlite.org:8080/cgi-bin/mailman/listinfo/sqlite-users
