(1) By anonymous on 2021-05-12 07:25:15 [link]
I'm a CS student and I'm doing some research on index Btree of SQLite. I have read the documentation and my questions are: - Is there a solution I can use to know the number of pages of Index Btree based on the number of entries and byte length of entries? (Assume that I create a database that has a table (indexed) of 1 column containing numbers) - Can I determine the degree of pages based on these features above?
(2) By curmudgeon on 2021-05-12 11:15:09 in reply to 1 [link]
Would this help? https://sqlite.org/dbstat.html
(3) By anonymous on 2021-05-12 12:35:26 in reply to 2 [link]
I mean can I predict based on the number of entries and byte length of entries without using that table?
(4) By Richard Hipp (drh) on 2021-05-12 14:45:38 in reply to 3 [link]
The byte-length of each index entry is (probably) different. You can't easily know what that byte-length is. CS textbook treatment of b-trees typically assumes each entry within a single b-tree is the same size in bytes. The b-tree is much easier to explain and analyze that way. But in the real world, data sizes vary. So the entry sizes vary. Any particular page of a b-tree might have just a single entry or it might have thousands of entries, depending on how many will fit. And the number of entries per page can vary widely among pages in the same b-tree. So, for SQLite, if you want to know: 1. The number entries in a b-tree 2. The sizes of all entries in the b-tree 3. The depth of the b-tree 4. The number of pages in the b-tree Then you have to walk the b-tree. There are no shortcuts.
(5) By Kees Nuyt (knu) on 2021-05-12 15:06:25 in reply to 1
I guess it would be possible to make a reasonable estimate using the [file format specification] in the documentation, but it will not be easy. Additionally, you may want to study the [btree source code], and other sources. All sources have a lot of informative and accurate comments. Note that integer numbers are stored in a [compact form], so low values consume fewer bytes than high values. If you develop an algorithm, it would make sense to verify its validity with sqlite3_analyzer, which is available in the [sqlite-tools download] for your platform, or can be complied from source. : https://www.sqlite.org/fileformat2.html#b_tree_pages : https://www.sqlite.org/cgi/src/file?udc=1&ln=on&ci=trunk&name=src%2Fbtree.c : https://www.sqlite.org/cgi/src/file?ci=trunk&name=src/util.c&ln=895-913 : https://www.sqlite.org/download.html