retrieve more than 5 K record

    public static EntityCollection paginationQuery (OrganizationServiceProxy _service, QueryExpression query)
        {
            int queryCount = 2500;
            int pageNumber = 1;
            int recordCount = 0;
            query.PageInfo = new PagingInfo();
            query.PageInfo.Count = queryCount;
            query.PageInfo.PageNumber = pageNumber;
            query.PageInfo.PagingCookie = null;
            EntityCollection fullResult = new EntityCollection();

            while (true)
            {
                // Retrieve the page.
                EntityCollection results = _service.RetrieveMultiple(query);
                
                if (results.Entities != null)
                {
                    // Retrieve all records from the result set.
                    foreach (var rec in results.Entities)
                    {
                        fullResult.Entities.Add(rec);
                        
                    }
                }

                // Check for more records, if it returns true.
                if (results.MoreRecords)
                {                    
                    // Increment the page number to retrieve the next page.
                    query.PageInfo.PageNumber++;
                    // Set the paging cookie to the paging cookie returned from current results.
                    query.PageInfo.PagingCookie = results.PagingCookie;
                }
                else
                {
                    return fullResult;
                    // If no more records are in the result nodes, exit the loop.
                    break;
                }
                
            }
            return fullResult;
        }