Hi Amit,
Sorry for the late reply on this. Looks like you need to allocate more memory… With 1K memory-size you will not be able to hold many records… Only 16 actually (each record uses 64bytes of RAM for the index). You will likely be able to go beyond (based on periodic checks for this) but the system will fairly quickly put you in stop-writes because you would be above the stop-writes-pct (default 90% of memory allocated). At that point, the database is putting itself in read-only mode to avoid using too much more memory then allocated. You can verify this in the logs (you would need to share more of the logs for me to point out where).
You can find more details on stop writes scenarios here.
Also, here is our capacity planning guide where you can find details on primary index sizing and more.
Thanks, and let us know if you have any further questions.
–meher