Using 10 threads i do writes to 4 RS using YCSB. The table created has 200 regions. In one of the run with 0.98 server and 0.98 client I faced this problem like the hlogs became more and the system requested flushes for those many regions.
One by one everything was flushed except one and that one thing remained unflushed. The ripple effect of this on the client side
On one of the RS
I restarted another RS and there were region movements with other regions but this region stays with the RS that has this issue. One important observation is that in HRegion.internalflushCache() we need to add a debug log here
Because we can see that the region is requsted for a flush but it does not happen and no logs related to flush are printed in the logs. so due to some reason this memstore.size() has become 0( I assume this). The earlier bugs were also due to similar reason.