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From "Luo Chen (Code Review)" <do-not-re...@asterixdb.incubator.apache.org>
Subject Change in asterixdb[master]: Avoid always merging old components in prefix policy
Date Sat, 10 Jun 2017 01:10:02 GMT
Luo Chen has posted comments on this change.

Change subject: Avoid always merging old components in prefix policy
......................................................................


Patch Set 5:

(1 comment)

> (5 comments)

https://asterix-gerrit.ics.uci.edu/#/c/1818/5/hyracks-fullstack/hyracks/hyracks-storage-am-lsm-common/src/main/java/org/apache/hyracks/storage/am/lsm/common/impls/PrefixMergePolicy.java
File hyracks-fullstack/hyracks/hyracks-storage-am-lsm-common/src/main/java/org/apache/hyracks/storage/am/lsm/common/impls/PrefixMergePolicy.java:

PS5, Line 303:  // otherwise, we can look ahead to see if adding more younger components
             :                     // could pass the ratio check.
> It looks to me that the old algorithm is O(2*n) for the worst case. However
I haven't done any profiling yet, but seems to me this is not a big problem for the following
reasons.

First, the new algorithm skips all too large disk components (just like the old algorithm).
Then it checks the remaining disk components to merge.
The key point is that the number of the remaining components is very small, basically similar
to maxToleranceComponentCount (normally 5 to 10 maybe?). It has optimizations to stop early
for most cases. I think it should be fine, given the actual number components we need to look
at is often very small.


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Gerrit-MessageType: comment
Gerrit-Change-Id: I464da3fed38cded0aee7b319a35664eae069a2ba
Gerrit-PatchSet: 5
Gerrit-Project: asterixdb
Gerrit-Branch: master
Gerrit-Owner: Luo Chen <cluo8@uci.edu>
Gerrit-Reviewer: Ian Maxon <imaxon@apache.org>
Gerrit-Reviewer: Jenkins <jenkins@fulliautomatix.ics.uci.edu>
Gerrit-Reviewer: Jianfeng Jia <jianfeng.jia@gmail.com>
Gerrit-Reviewer: Luo Chen <cluo8@uci.edu>
Gerrit-Reviewer: Yingyi Bu <buyingyi@gmail.com>
Gerrit-Reviewer: abdullah alamoudi <bamousaa@gmail.com>
Gerrit-HasComments: Yes

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