KinoSe...eFormat(3pm)

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version 1.01 · 8 versions
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💖 KinoSe...eFormat(3pm) 💖

okay so bestie, welcome to the User Contributed Perl Documentation page for this one. Grab a strawberry 🍓, we're gonna talk about file formats.

✨ NAME ✨

KinoSearch1::Docs::FileFormat — the lowdown on the invindex file format, fr fr.

🌈 OVERVIEW 🌈

ngl, you do not have to understand the guts of the Lucene-derived invindex file format to actually use KinoSearch1. Like, not even a little. But it might be helpful if you're into tweaking stuff for high performance, doing some exotic usage, or you're debugging and developing. iykyk 👑

So. On a file system, all the files in an invindex live in one, flat directory. But conceptually they have a hierarchical relationship: an invindex is made up of "segments", each segment is its own independent inverted index, and each segment is made up of several subsections. it's giving family tree 🌳

[invindex]--|
            |-"segments" file
            |
            |-[segments]------|
                              |--[seg _0]--|
                              |            |--[postings]
                              |            |--[stored fields]
                              |            |--[deletions]
                              |
                              |--[seg _1]--|
                              |            |--[postings]
                              |            |--[stored fields]
                              |            |--[deletions]
                              |
                              |--[ ... ]---|

The "segments" file keeps a list of the segments that make up an invindex. Here's the tea: when a new segment is being written, KinoSearch1 may put files into the directory, but until the segments file is updated, a Searcher reading the index won't know about them. so sneaky 🙈

Each segment is an independent inverted index. All the files which belong to a given segment share a common prefix, and that prefix is an underscore followed by 1 or more decimal digits: _0, _67, _1058. A fully optimized index has only a single segment — main character energy, honestly. 💅

In theory there are many files which make up each segment. However, when you look inside an invindex that's not in the process of being updated, you'll probably see only the segments file and files with either a .cfs or .del extension. The .cfs file, a "compound" file which is consolidated when a segment is finalized, "contains" all the other per-segment files.

Segments are written once, and with the exception of the deletions file, are never modified once written. They are deleted when their data is written to new segments during the process of optimization.

🦋 A segment's component parts 🦋

Each segment can be said to have four logical parts: postings, stored fields, the deletions file, and the term vectors data. four, iconic, no notes.

🎀 Stored fields 🎀

The stored fields are organized into two files.

  • [seg_name].fdx - Field inDeX - pointers to field data
  • [seg_name].fdt - Field DaTa - the actual stored fields

When a document turns up as a hit in a search and must be retrieved, KinoSearch1 looks at the Field inDeX file to see where in the data file the document's stored fields start, then retrieves all of them from the .fdt file in one lump. one lump, one trip, slay. ✨

_1.fdx--|
        |--[doc#0  =>   0]----->_1.fdt--|
        |                               |--[bodytext]
        |                               |--[title]
        |                               |--[url]
        |--[doc#1  => 305]----->_1.fdt--|             # byte 305
        |                               |--[bodytext]
        |                               |--[title]
        |                               |--[url]
        |--[...]--------------->_1.fdt--|--[...]

If a field is marked as "vectorized", its "term vectors" are also stored in the .fdx file. lil bonus content 🫶

🔥 Postings 🔥

"Posting" is a technical term from the field of Information Retrieval which refers to an single instance of a one term indexing one document. Say you're looking at the index in the back of a book, and you see that "freedom" is referenced on pages 8, 86, and 240 — that's three postings, and taken together they form a "posting list". Same terminology applies to an index in electronic form. periodt.

The postings data is spread out over 4 main files (not including field normalization data, which we'll get to in a moment). From lowest to highest in the hierarchy, they are...

[seg_name].prx - PRoXimity data. A list of the positions at which terms appear in any given document. The .prx file is just a raw stream of VInts; the document numbers and terms are implicitly indicated by files higher up the hierarchy.

[seg_name].frq - FReQuency data for terms. If a term has a frequency of 5 in a given document, that implies that there will be 5 entries in the .prx file. The terms themselves are implicitly specified by the .tis file.

_1.frq--|
        |--[doc#40 => 2]----->_1.prx--|--[54,107]
        |--[doc#0  => 1]----->_1.prx--|--[6]
        |--[doc#6  => 1]----->_1.prx--|--[504]
        |--[doc#36 => 3]----->_1.prx--|--[2,33,747]
        |--[...]------------->_1.frq--|--[...]

[seg_name].tis - TermInfoS. Among the items stored here is the term's doc_freq, which is the number of documents the term appears in. If a term has a doc_freq of 22 in a given collection, that implies that there will be 22 corresponding entries in the .frq file. Terms are ordered lexically, first by field, then by term text.

_1.tis--|
        |--[...]----------------------->_1.frq--|--[...]
        |--[bodytext:mule      =>  1]-->_1.frq--|--[doc#40 => 2]
        |--[bodytext:multitude =>  3]-->_1.frq--|--[doc#0  => 1]
        |                                       |--[doc#6  => 1]
        |                                       |--[doc#36 => 3]
        |--[bodytext:navigate  =>  1]-->_1.frq--|--[doc#21 => 1]
        |--[...]----------------------->_1.frq--|--[...]
        |--[title:amendment    => 27]-->_1.frq--|--[doc#21 => 1]
        |                                       |--[doc#22 => 1]
        |--[...]----------------------->_1.frq--|--[...]

[seg_name].tii - TermInfos Index. This file, which is decompressed and loaded into RAM as soon as the IndexReader is initialized, contains a small subset of the .tis data, with pointers to locations in the .tis file. It is used to locate the right general vicinity in the .tis file as quickly as possible. speed demon behavior ⚡

_1.tii--|
        |--[bodytext:a => 20]---------->_1.tis--|--[bodytext:a] # byte 20
        |                                       |--[bodytext:about]
        |                                       |--[bodytext:absolute]
        |                                       |--[...]
        |--[bodytext:mule => 27065]---->_1.tis--|--[bodytext:mule]
        |                                       |--[bodytext:multitude]
        |                                       |--[...]
        |--[title:amendment => 56992]-->_1.tis--|--[title:amendment]
                                                |--[...]

Here's a simplified version of how a search for "freedom" against a given segment plays out. think of it as a group chat between files 💬

  1. The searcher asks the .tii file, "Do you know anything about 'freedom'?" The .tii file replies, "Can't say for sure, but if the .tis file does, 'freedom' is probably somewhere around byte 21008".
  2. The .tis file tells the searcher "Yes, we have 2 documents which contain 'freedom'. You'll find them in the .frq file starting at byte 66991."
  3. The .frq file says "document number 40 has 1 'freedom', and document 44 has 8. If you need to know more, like if any 'freedom' is part of the phrase 'freedom of speech', take a look at the .prx file starting at..."
  4. If the searcher is only looking for 'freedom' in isolation, that's where it stops. It already knows enough to assign the documents scores against "freedom", with the 8-freedom document scoring higher than the single-freedom document.

💀 Deletions 💀

When a document is "deleted" from a segment, it is not actually purged from the postings data and the stored fields data right away; it is merely marked as "deleted", via the .del file. The .del file contains a bit vector with one bit for each document in the segment; if bit #254 is set then document 254 is deleted, and if it turns up in a search it will be masked out. masked, not gone. the audacity 😭

It is only when a segment's contents are rewritten to a new segment during the segment-merging process that deleted documents truly go away.

🌸 Field Normalization Files 🌸

For the sake of simplicity, the example search scenario above omits the role played by the field normalization files, or "fieldnorms" for short. These files have the (theoretical) suffix of .f followed by an integer -- .f0, .f1, etc. Each segment contains one such file for every indexed field.

By default, the fieldnorms' job is to make sure that a field which is 100 terms long and contains 10 mentions of the word 'freedom' scores higher than a field which also contains 10 mentions of the word 'freedom', but is 1000 terms in length. The idea is that the higher the density of the desired term, the more relevant the document. density = relevance, we love a proportional queen 👑

The fieldnorms files contain one byte per document per indexed field, and all of them must be loaded into RAM before a search can be executed. so don't go feral with your indexed fields, bestie.

🧚 Document Numbers 🧚

Document numbers are ephemeral. They change every time a document gets moved from one segment to a new one during optimization. If you need to assign a primary key to each document, you need to create a field and populate it with an externally generated unique identifier. they will not stay put, they are not loyal, do not trust them fr. 🙈

⭐ Not compatible with Java Lucene ⭐

The file format used by KinoSearch1 is closely related to the Lucene compound index format. (The technical specification for Lucene's file format is distributed along with Lucene.) However, indexes generated by Lucene and KinoSearch1 are not compatible. they're cousins, not twins. do not try to make them swap clothes. 💀

Copyright 2005-2010 Marvin Humphrey

📜 LICENSE, DISCLAIMER, BUGS, etc. 📜

See KinoSearch1 version 1.01.

and that's the whole page, bestie! 🎀 this one came from <rainbow>perl v5.42.3</rainbow>, dated 2026-08-20 💖 thanks for reading all the way to the bottom, you're literally the best. mwah! 🫶✨

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