plan 9: keyword cache keys on extension, max-read and Unicode tables, trims removed keywords

1 files changed, 17 insertions, 11 deletions

diff --git a/docs/design.md b/docs/design.md
index caa2a0f..bea0e2f 100644
--- a/docs/design.md
+++ b/docs/design.md
@@ -336,9 +336,11 @@ Extraction is nearly all of a run's time, so krino remembers what it found.
 For each file it extracted, `<name>.cache` records which of the
 directory's content keywords the text contains, against the full list of
 keywords it was checked against. It stores no text and no file names; a
-file is known by device, inode, size and modification time, which krino's
-own moves and renames keep. The keywords themselves are stored, as they
-appear in the config.
+file is known by device, inode, size, modification time and extension
+(the extension picks the extractor), which a move within one filesystem
+keeps. The keywords themselves are stored, normalised the way the test
+compares them (case, folding, whitespace), and only those the directory
+still uses.
 
 - When a file is extracted, every content keyword of its directory is
   answered at once, so one extraction serves every rule and exclude.
@@ -347,16 +349,20 @@ appear in the config.
   replaced: a changed file, or a new keyword, costs one extraction.
 - Files above `max-read` are refused before the cache is consulted.
   Failures (unreadable, tool missing, timeout) are never cached.
-- The cache is discarded whole when the extractor fingerprint changes: a
-  tool installed, removed or replaced, or krino's extraction code changing
-  (`extract.Version`), or its text normalisation changing (`norm.Version`).
+- The cache is discarded whole when its fingerprint changes: a tool
+  installed, removed or replaced; krino's extraction code (`extract.Version`)
+  or normalisation (`norm.Version`) changing; the Go release or the Unicode
+  tables changing; or the directory's `max-read` changing.
 - Planning a run (`-n` included) reads the cache and writes it back holding
   only files still in the directory, under the directory's lock, via a
-  temporary file renamed into place; the directory is 0700, the file 0600.
-  `explain` reads it and never writes. A directory with no content tests
-  has no cache.
-- Known gap: a file edited in place with its size and modification time
-  deliberately preserved keeps its old answers. Deleting
+  temporary file renamed into place; the directory is made 0700, the file
+  0600. `explain` reads it and never writes. A directory with no content
+  tests has no cache, and an old one is removed.
+- Known gaps: a file edited in place with its size and modification time
+  deliberately preserved keeps its old answers, and so does a new file that
+  reuses a deleted file's inode with the same size, extension and preserved
+  modification time. A `.doc` that `antiword` failed on (a timeout, say) and
+  `catdoc` then read is cached with `catdoc`'s answers. Deleting
   `~/.cache/krino` resets everything.
 
 ## 7. Actions