Why mincore() returns different value of stat ?Hiroaki Kubota
Analyzer of MongoDB 2.4 's new feature returned ununderstandable results.
The value of "resident" totally different from "pagesInMemory".
But why ?
-"resident" are coming from STAT.
-"pageInMemory" are coming from mincore().
This slide illustrates this issue.
This document discusses ghost sync and slave delay in MongoDB replica sets. Ghost sync allows secondaries to sync from each other to improve availability when the primary is unavailable or when a secondary is catching up. Slave delay intentionally delays a secondary from syncing data from the primary for a set time period to serve as a backup in case of human errors. However, using a slave delay secondary as a ghost target is problematic as its oplog will always be delayed from the primary.
1. MongoDB's default indexing method causes performance issues as it locks the entire replica set during indexing.
2. Background indexing in newer versions may help but still risks slowing down all secondaries simultaneously.
3. The presenter suggests a manual indexing method where each secondary can index independently without affecting the others. This would distribute the indexing load and prevent replica set-wide slowdowns.
29. MongoDBのスループット
Range fetch (10,000件 x 100)
SELECT
・MySQL
: 202 sec
*
FROM
・MongoDB : 3.7 sec
mytbl
WHERE
id BETWEEN 0 AND 9999;
Range count (10,000件 x 100)
・MySQL
: 37 sec
SELECT
COUNT(*)
・MongoDB : 0.4 sec
FROM
mytbl
WHERE
id BETWEEN 0 AND 9999;