##Why replica record count might appear to drop suddenly during migrations
Issue: During migration replica record count appears to change when node is viewed via:
asadm -e info
When nodes are migrating partitions, the replica record count drops, sometimes severely, an extreme example is shown below.
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~Namespace Information~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Node Namespace Avail% Evictions Master Replica Repl Stop Migrates Disk Disk HWM Mem Mem HWM Stop . . . . Objects Objects Factor Writes (tx,rx) Used Used% Disk% Used Used% Mem% Writes% aero-10:3000 persistent 32 206131141 1.754 G 0.000 2 false (N/E,N/E) 1.841 TB 48 75 210.635 GB 61 65 90 aero-11:3000 persistent 37 0 1.646 G 0.000 2 false (N/E,N/E) 1.724 TB 45 75 197.253 GB 57 65 90 aero-12:3000 persistent 35 0 1.821 G 0.000 2 false (N/E,N/E) 1.767 TB 46 75 202.210 GB 58 65 90
The overall number of records, shown in the statistic record_refs will reflect the correct value (correct number of master records + correct number of prole records). Record_refs is defined as the number of index records currently referenced, the total number of records across the cluster.
This is expected behaviour. The objects of desynchronised replica partitions are not counted until they become synchronised. This means that if a partition is not the master or acting master and has an inbound migration, the objects in that partition will not be counted, and so we may see a sharp drop in replica record numbers. This can be particularly obvious when a specific node has a high number of outbound migrations. In that scenario the other nodes in the cluster would have a high number of scheduled inbound migrations and the replica objects would not be counted.
This is normal behaviour and as long as record_refs reflects the total number of master and replica records in the cluster there is no issue. The replica record count per node will stabilise once migrations are completed.