Key Value Storage
Understanding the Functionality of CW Key-Value Storage
As previously highlighted, the key-value storage mechanism in Cosmos-SDK operates on the premise that each value is stored under a corresponding key.
This storage system is organized within a tree structure, specifically following the cosmos/iavl tree model.
To understand the workings of this key-value storage approach, let's delve into its mechanics:
In order to facilitate your understanding of KV store iterators, let's employ a highly simplified analogy. Imagine letters enclosed within circles, where each letter represents a key, and each key is associated with a corresponding value.
Let's continue by considering a set of saved key-value pairs:
J -> value1
JF -> value2
JPV -> value3
JPVA -> value4
JPVD -> value5
JPVX -> value6
Fetching a Single Value with a Known Key is an Efficient O(1) Operation. However, When Navigating Through a Set of Keys, It's Achieved Through Prefix-Based Iteration.
J key, prefixes: J
JF key, prefixes: J, JF
JPV key, prefixes: J,JP, JPV
JPVA key, prefixes: J,JP, JPV, JPVA
JPVD key, prefixes: J,JP, JPV, JPVD
JPVX key, prefixes: J,JP, JPV, JPVX
range(J) returns all keys because all have J as prefix range(JF) returns only JF
This is where it gets intriguing.: range(JPV) returns JPV, JPVA, JPVD, JPVX in order As you can see J or JF is not returned, because values after JPV is requested.
But Why Was JPVA Returned?
The keys stored in the database are in the form of fixed-length strings. For instance, if we assume that keys are uniformly 8 characters in length, the storage representation of "JPVA" would be "JPVA0000".
When a range request is initiated, the underlying process systematically iterates over all keys within a specific range, starting from "JPV00000" and concluding at "JPVFFFFF." In this case, "JPVA" (among other keys) naturally falls within this range. It's important to note that a range query can also be executed in reverse, offering flexibility in key retrieval.
We have two fundamental operations at play: Retrieving Individual Values and Iterating
There are just two core functionalities in operation: fetching a single value or navigating through a collection of keys. While data structures often require intricate relationships, we work within the confines of this constrained key-value storage, where these two fundamental operations are paramount.
This is accomplished through the construction of indexes.
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