branch: elpa/flx
commit 4c67675437e9c2e338f091322bb967ba93f2d86d
Author: Le Wang <le.w...@agworld.com.au>
Commit: Le Wang <le.w...@agworld.com.au>
add GC tuning information to README
---
README.md | 55 +++++++++++++++++++++++++++++++++++++++++++++++++++++++
1 file changed, 55 insertions(+)
diff --git a/README.md b/README.md
index b6c1eeb3e5..f1b3e5bc26 100644
--- a/README.md
+++ b/README.md
@@ -7,6 +7,61 @@ It's unlikely to crash your Emacs, but do expect to encounter
bugs.
[Screencast showing rationale and ido workflow][]
+# Memory Usage
+
+The flx algorithm willingly sacrifices memory usage for speed.
+
+For 10k file names, about 10 MB of memory will be used to speed up future
+matching. This memory is never released to keep the match speed fast.
+
+So far with modern computers, this feels like a reasonable design decision.
+
+It may change in future.
+
+
+# GC Optimization
+
+Emacs garbage collector is fairly primitive stop the world type. GC time can
+contribute significantly to the run-time of computation that allocates and
+frees a lot of memory.
+
+Consider:
+
+ (defun uuid ()
+ (format "%08x-%08x-%08x-%08x"
+ (random (expt 16 4))
+ (random (expt 16 4))
+ (random (expt 16 4))
+ (random (expt 16 4))))
+
+ (benchmark-run 1
+ (let ((cache (flx-make-filename-cache)))
+ (dolist (i (number-sequence 0 10000))
+ (flx-process-cache (uuid) cache))))
+ ;;; ⇒ (0.899678 9 0.33650300000000044)
+
+This means that roughly 30% of time is spent just doing garbage-collection.
+
+`flx` can benefit significantly from garbage collection tuning.
+
+By default Emacs will initiate GC every 0.76 MB allocated (`gc-cons-threshold`
+== 800000). If we increase this to 20 MB (`gc-cons-threshold` == 20000000)
+
+We get:
+
+ (benchmark-run 1
+ (setq gc-cons-threshold 20000000)
+ (let ((cache (flx-make-filename-cache)))
+ (dolist (i (number-sequence 0 10000))
+ (flx-process-cache (uuid) cache))))
+ ;;; ⇒ (0.62035 1 0.05461100000000041)
+
+So if you have a modern machine, I encourage you to add
+
+ (setq gc-cons-threshold 20000000)
+
+to your init file.
+
# ido support
Add this to your init file and *flx* match will be enabled for ido.
