c# - Fast access to key in file (without loading whole file to memory) -

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background: writing c# application windows mobile search definitions (scientific) dictionary filesystem. file looks (file has 100k+ entries):

 word1:meanings(2) -meaning 1 bla bla bla -meading 2 bla bla bla [...]

the user should able enter word , meaning fast possible. users 1 or 2 words. this, created second file sorted list actual word , byte-offset in dictionary file. example:

word1:12344 word2:32241 word3:298

i through "index" (simple loop through lines , compare if equal) , "random-access" dictionary file using byte-offset. problem is, still slow. tried loading index array/list/hashtable due slow io, takes long (about 20 seconds load index). bad because user 1 word. therefore, looking type of n-tree implementation can work directly on file (without traversing whole index). has advise how this? current solution looks (but buggy , dirty): new index has format:

a:fileoffsetindictionary:fileoffsetof"ab" //the first 2 character starting b:fileoffsetindictionary:fileoffsetof"ba" c:fileoffsetindictionary:0 //"0" means no words starting "c" (just example) [...] ab:fileoffsetindictionary:fileoffsetof"aba" ac:fileoffsetindictionary:878878 //(just random values illustration) [...] ba:fileoffsetindictionary:456 [...] aba:fileoffsetindictionary:2342 [...]

and searching done way:

users enter word "tree" "t" in index looping through index if "t" found goto fileoffsetof2digit if "tr" found goto fileoffsetof3digit [...] [actually recursively coded]

the correct answer tell use b-tree index ideal disk based index of nature, or better yet if talking mobile 6.5 , earlier use sql ce database. , can find number of implementations, failing following.

using along lines of current index file idea, make each index record fixed size. if know word never more 50 char , offset fit in 4 byte integer, can create record entries in index file 54 bytes (assuming ascii words, adjust accordingly). can perform binary search on index file rather scaning entire file access each record.


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