Function getShardSizeBounds

fdbserver/DataDistributionTracker.actor.cpp:146–178

Gets the permitted size and IO bounds for a shard. A shard that starts at allKeys.begin (i.e. '') will have a permitted size of 0, since the database can contain no data.

// Gets the permitted size and IO bounds for a shard. A shard that starts at allKeys.begin
//  (i.e. '') will have a permitted size of 0, since the database can contain no data.
ShardSizeBounds getShardSizeBounds(KeyRangeRef shard, int64_t maxShardSize) {
	ShardSizeBounds bounds;

	if (shard.begin >= keyServersKeys.begin) {
		bounds.max.bytes = SERVER_KNOBS->KEY_SERVER_SHARD_BYTES;
	} else {
		bounds.max.bytes = maxShardSize;
	}

	bounds.max.bytesPerKSecond = bounds.max.infinity;
	bounds.max.iosPerKSecond = bounds.max.infinity;
	bounds.max.bytesReadPerKSecond = bounds.max.infinity;

	// The first shard can have arbitrarily small size
	if (shard.begin == allKeys.begin) {
		bounds.min.bytes = 0;
	} else {
		bounds.min.bytes = maxShardSize / SERVER_KNOBS->SHARD_BYTES_RATIO;
	}

	bounds.min.bytesPerKSecond = 0;
	bounds.min.iosPerKSecond = 0;
	bounds.min.bytesReadPerKSecond = 0;

	// The permitted error is 1/3 of the general-case minimum bytes (even in the special case where this is the last
	// shard)
	bounds.permittedError.bytes = bounds.max.bytes / SERVER_KNOBS->SHARD_BYTES_RATIO / 3;
	bounds.permittedError.bytesPerKSecond = bounds.permittedError.infinity;
	bounds.permittedError.iosPerKSecond = bounds.permittedError.infinity;
	bounds.permittedError.bytesReadPerKSecond = bounds.permittedError.infinity;

	return bounds;
}

int64_t getMaxShardSize(double dbSizeEstimate) {
	return std::min((SERVER_KNOBS->MIN_SHARD_BYTES + (int64_t)std::sqrt(std::max<double>(dbSizeEstimate, 0)) *