We are using MongoDB 4.2 which has lot of collections and indexes. Yesterday we faced issue in which our mongodb started degraded performance where query which were taking few ms started taking thousands of ms.
Upon observing metrics in datadog, during incident we observed that
datasize in replicaset parameter in datadog was showing lost of data from 90GB to 8GB.
We are looking for reason what can cause sudden drop in the replicaset Datasize changes or any other way from logs to debugg it. As in the logs we were not able to get anything apart from the slow query performance.
Appreciate your help in advance.