Which approach is optimal for implementing server-side pagination with MatTableDataSource?

The Optimal Approach: Custom DataSource

The optimal approach for server-side pagination is to abandon MatTableDataSource and instead implement a custom class that extends the DataSource base class. Because MatTableDataSource is architected specifically for local arrays, attempting to force it to handle server-side streams often leads to redundant state management and memory inefficiency.

Implementation Logic

By extending DataSource<T>, you gain direct control over the connect() method, allowing you to treat pagination and sorting events as a combined stream of triggers for your API calls.

1. Create a Custom DataSource: Define a class that implements connect(). This method should return an Observable<T[]>.
2. Merge Event Streams: Use merge() to combine the paginator.page and sort.sortChange observables. This ensures that any change in page index, page size, or sort order triggers a new request.
3. Handle Data Fetching: Use the switchMap operator to call your backend service. This cancels pending requests if a user clicks the paginator rapidly.
4. Synchronize Total Count: Update the MatPaginator.length property using the total record count returned by your server response. This is critical for the paginator to calculate the total number of pages correctly.

Example Implementation Pattern

// Simplified DataSource logic
connect() {
  return merge(this.paginator.page, this.sort.sortChange).pipe(
    startWith({}),
    switchMap(() => {
      return this.apiService.getData(
        this.paginator.pageIndex,
        this.paginator.pageSize,
        this.sort.active,
        this.sort.direction
      ).pipe(
        tap(response => this.paginator.length = response.totalCount)
      );
    })
  );
}

Verification Steps

• Network Inspection: Verify that changing a page or sort column triggers a single HTTP request containing only the requested subset of data, not the full dataset.
• State Sync: Confirm that the MatPaginator "Last Page" button correctly reflects the server-provided total count.
• Race Conditions: Rapidly click pagination buttons to ensure switchMap is correctly discarding stale responses.

Diagnostic Detail Needed: Does your backend API support a totalCount field in the same response as the data array, or is the count provided via a separate header/endpoint? This determines whether you can update the paginator length within a single tap operator or if a secondary request is required.