Mini Cassandra
Cassandra is a NoSQL storage. The structure has two-level keys.
Level 1: raw_key. The same as hash_key or shard_key.
Level 2: column_key.
Level 3: column_value
raw_key is used to hash and can not support range query. let's simplify this to a string.
column_key is sorted and support range query. let's simplify this to integer.
column_value is a string. you can serialize any data into a string and store it in column value.
implement the following methods:
- insert(raw_key, column_key, column_value)
- query(raw_key, column_start, column_end) // return a list of entries
Example
insert("google", 1, "haha")
query("google", 0, 1)
>> [(1, "haha")]
/**
* Definition of Column:
* public class Column {
* public int key;
* public String value;
* public Column(int key, String value) {
* this.key = key;
* this.value = value;
* }
* }
*/
public class MiniCassandra {
private Map<String, NavigableMap<Integer, String>> map;
public MiniCassandra() {
map = new HashMap<>();
}
/**
* @param raw_key a string
* @param column_start an integer
* @param column_end an integer
* @return void
*/
public void insert(String raw_key, int column_key, String column_value) {
if (!map.containsKey(raw_key)) {
map.put(raw_key, new TreeMap<Integer, String>());
}
map.get(raw_key).put(column_key, column_value);
}
/**
* @param raw_key a string
* @param column_start an integer
* @param column_end an integer
* @return a list of Columns
*/
public List<Column> query(String raw_key, int column_start, int column_end) {
List<Column> result = new ArrayList<>();
if (map.containsKey(raw_key)) {
NavigableMap<Integer, String> nm = map.get(raw_key).subMap(column_start, true,
column_end, true);
for (Map.Entry<Integer, String> entry : nm.entrySet()) {
result.add(new Column(entry.getKey(), entry.getValue()));
}
}
return result;
}
}
Hope this helps,
Michael