src/ab/plugins/db/rds.py [404:424]:
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        sample = self.db.table_sql(sql, table_name)
        logger.debug('try to sample {mk} rows'.format(mk=mk))
        logger.debug('run sql:', sql)
        logger.debug('get sample count:', len(sample))

        # step 2: sample self.max_count rows
        if len(sample) > self.max_count:
            sample = random.sample(sample, self.max_count)
        row_count = len(sample)
        return 100.0 * row_count / total_count, row_count, sample


class HeadSampler(Sampler):
    def sample(self, table_name: str, total_count: int):
        '''
        args:
            total_count: total row count of target partitions or whole table
        returns:
            sample_rate, sample_count, sample_data
        '''
        assert total_count > self.max_count, 'system error, total_count must be greater than sampler max_count'
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src/ab/plugins/db/sqlite.py [379:399]:
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        sample = self.db.table_sql(sql, table_name)
        logger.debug('try to sample {mk} rows'.format(mk=mk))
        logger.debug('run sql:', sql)
        logger.debug('get sample count:', len(sample))

        # step 2: sample self.max_count rows
        if len(sample) > self.max_count:
            sample = random.sample(sample, self.max_count)
        row_count = len(sample)
        return 100.0 * row_count / total_count, row_count, sample


class HeadSampler(Sampler):
    def sample(self, table_name: str, total_count: int):
        '''
        args:
            total_count: total row count of target partitions or whole table
        returns:
            sample_rate, sample_count, sample_data
        '''
        assert total_count > self.max_count, 'system error, total_count must be greater than sampler max_count'
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