#!/usr/bin/env python
#
# Public Domain 2014-present MongoDB, Inc.
# Public Domain 2008-2014 WiredTiger, Inc.
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# test_cursor15.py
#   Cursors: read_once configuration
#

import wttest
from wiredtiger import stat

class test_cursor15(wttest.WiredTigerTestCase):
    tablename = 'test_read_once'
    uri = 'table:' + tablename

    conn_config = 'cache_size=1M'

    def test_cursor15(self):
        # This test is configured to use 1MB of cache. It will insert 20
        # documents, each 100KB. Manipulate the table to result in one page per
        # document.
        self.session.create(self.uri,
            'key_format=i,value_format=S,leaf_page_max=108K,leaf_value_max=108K')

        cursor = self.session.open_cursor(self.uri, None, None)
        for key in range(0, 20):
            cursor[key] = '1' * (100 * 1024)
        cursor.close()

        # Restart the database to clear the cache.
        self.reopen_conn()

        # We don't restart the database between runs to exercise that read_once
        # plays nice with cursor caching. Note, there are no reliable statistics
        # to check that read_once behaves as expected. The future may introduce a
        # statistic for WT_READ_WONT_NEED being exercised. That may work as a
        # suitable side-effect to observe here.
        for cursor_conf in ["read_once=true", None]:
            # Table scan ~2MB of data when only given 1MB of cache.
            cursor = self.session.open_cursor(self.uri, None, cursor_conf)
            for key, value in cursor:
                pass
            cursor.close()

if __name__ == '__main__':
    wttest.run()
