Cursor Class

1public with sharing class QueryChunkingQueueable implements Queueable {
2    private Database.Cursor locator;
3    private Integer position;
4
5    public QueryChunkingQueueable() {
6        locator = Database.getCursor(
7            'SELECT Id FROM Contact WHERE LastActivityDate = LAST_N_DAYS:400',
8            AccessLevel.USER_MODE);
9        position = 0;
10    }
11
12    public void execute(QueueableContext ctx) {
13        Integer remainingRows = locator.getNumRecords() - position;
14        if (remainingRows == 0) {
15            return; // Nothing to do
16        }
17
18        // Take the minimum of batch size and remaining rows to avoid over-fetching
19        Integer fetchSize = Math.min(200, remainingRows);
20
21        List<Contact> scope = locator.fetch(position, 200);
22        position += scope.size();
23        // do something, like archive or delete the scope list records
24        if (position < locator.getNumRecords()) {
25            // process the next chunk
26            System.enqueueJob(this);
27        }
28    }
29}