Sidebar Conversation List Slow Initial Load: Hydration Issue Resolution

Ever been frustrated by a sluggish sidebar conversation list when it first pops up? Especially for a heavy user hopping into the app for the first time, that loading speed is their first impression, right? Today, I want to talk about how I tackled the initial loading performance of that very sidebar conversation list.

Attempts and Pitfalls

At first, I simply thought about reducing the number of conversations displayed in the sidebar. So, I changed the logic to show only the first 25 initially, and the rest would be loaded when the 'Show More' button was clicked.

// Initial conversation list rendering logic (simplified)
const initialConversations = conversations.slice(0, 25);
// ... render UI using initialConversations

Even though the amount of data was clearly reduced, strangely, I still felt a lag during the hydration process. The rendering itself seemed faster, but when the user tried to interact with something, there was a noticeable delay.

// Not an actual error message, but the symptom I felt at the time
// "Uncaught Error: Hydration failed because the initial UI does not match the server-rendered UI."
// Or simply slow UI response

I stared at it for a long time, wondering why this was happening when I had reduced the data. I was just guessing – perhaps unnecessary computations were running continuously within the component, or maybe it was clashing with another library. After about 3 hours of struggling, I finally found the cause.

The Cause

The problem was that simply reducing the amount of data loaded during the initial load wasn't enough. What I overlooked was that even with the reduced data, I was trying to calculate and prepare all the information contained within that data (e.g., last message content, read status, etc.) at the initial rendering point. In other words, while the data itself was less, the computational cost of processing that data was still high. This caused a bottleneck during hydration as it tried to perform all these computations at once.

The Solution

Ultimately, the solution was much simpler. For the initial load, I changed it to load only the absolute minimum information and dynamically load the rest of the detailed information when the user clicks on that conversation or scrolls down.

// Improved initial conversation list rendering logic (simplified)
const initialConversations = conversations.slice(0, 25).map(conv => ({
  id: conv.id,
  name: conv.name,
  // Detailed info like last message content, read status, etc., are not loaded here
}));
// Load detailed info when the user clicks a specific conversation or scrolls
function loadConversationDetails(conversationId) {
// Load detailed info via API call, etc.
// ...
}

By doing this, only the essential ID and name were loaded into memory during the initial render, making the hydration process significantly lighter.

The Results

• The initial entry experience for heavy users of the application has noticeably improved.
• Page loading speed became perceptibly faster, and UI responsiveness significantly increased.
• Previously, there were flickering or freezing issues during loading, but these have almost disappeared.

Summary — How to Avoid the Same Pitfall

• [ ] For components with a lot of data like sidebars or lists, design them to load only the absolute minimum information during initial loading.
• [ ] Consider a strategy where detailed information like last message content and read status is dynamically loaded based on user interaction (clicks, scrolls, etc.).
• [ ] Remember that beyond just the amount of data, the computational cost of processing each data item also impacts initial rendering performance.
• [ ] If you encounter hydration errors or reduced UI responsiveness, check not only the data volume but also the computational logic within the component.