From 55310a5309e944ac3d0bcf5668f35b9ab35824cd Mon Sep 17 00:00:00 2001 From: Michael Baird Date: Thu, 13 Jul 2017 09:32:47 -0500 Subject: [PATCH] frame cache caveats documentation --- docs/query-language.md | 8 ++++++++ 1 file changed, 8 insertions(+) diff --git a/docs/query-language.md b/docs/query-language.md index 5400c8ead..106bfb08f 100644 --- a/docs/query-language.md +++ b/docs/query-language.md @@ -341,6 +341,14 @@ have the attribute specified by `field` with one of the values specified in **Result Type:** array of key/count objects +**Caveats:** +* TopN will return the top bitmaps by count only on frames with a ranked cache. +* The frame's cache size determines the limit of sorted bitmaps. +* Non-ranked frames maintain a LRU (least recently used) cache, thus a TopN query on this frame will return bitmaps in most recently setbit order. +* The ranked cache maintains a sorted set of bitmaps by count up to the cache size. +* Once full, the cache will truncate the set of bitmaps at the frame options CacheSize limit. Bitmaps with a similar count that straddle the limit will be truncated in no particular order. +* The TopN filter operation only applies to data in the cache, and not all bitmaps in the frame. + **Examples:** ```