OpenEdge Data Management: DataServer for Microsoft SQL Server

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Initial Programming Considerations Cursors 2–48 A cursor is like a pointer that points to consecutive records in a table. The ABL uses cursors to keep track of where it is in a table; for example, when it processes FOR EACH statements. Suppose that you are reading records from the customer table using the custnum index, and your current record is customer number 50. This means that ABL has a cursor positioned at custnum 50. Note that ABL maintains cursor positioning across queries. The DataServer allows applications that access MS SQL Server data sources to imitate OpenEdge cursor behavior for FIND cursors. FOR EACH and OPEN QUERY statements do not retain cursor position across other queries or against a FIND statement. This section discusses the following cursor-related activities: • Forward and backward scrolling • Block cursors For details about firehose and fast forward-only cursors, see the “Firehose and Fast Forward-Only Cursors” section on page 4–5. Forward and backward scrolling A query is scrolling if you specify SCROLLING in the DEFINE QUERY statement or if you define a browse for the query. You can use the REPOSITION statement to change your current position with the result set. For a non-scrolling query, the DataServer allows you to only move sequentially forward through the rows by using the FIRST and options of the GET statement. Scrolling basically means that the result set is cached on the client for backward and forward scrolling. With the DataServer, forward and backward scrolling works with a MS SQL Server just as it does with an OpenEdge database except when the data source fails to find a record. In ABL, the cursor position can change after a failed search; however, with the DataServer, a failed search does not affect the cursor. For example, if a cursor is positioned at custnum 50 and a request for the next customer from an OpenEdge table fails, the cursor moves to the next sequential record beyond custnum 50. The same failed request from a data source leaves the cursor at custnum 50. Your DataServer applications should not assume a certain cursor position after a failed find. You can, however, still use the AVAILABLE function to determine whether a record is available. The AVAILABLE function behaves consistently whether it accesses an OpenEdge database or a MS SQL Server data source.
Impact of MAX-ROWS Cursors The MAX-ROWS qualifier on a query determines the number of rows returned. The MAX-ROWS calculation is applied before any sorting is applied to the query, causing the results to be random. Consider the following example: DEFINE QUERY x FOR customer SCROLLING. OPEN QUERY x FOR EACH customer MAX-R0WS 15. GET LAST x. DISPLAY customer.custnum. REPEAT: GET PREV x. DISPLAY customer.custnum. END. When this example is run with the OpenEdge sports database, the first record return has custnum 54, and the repeat loop displays other custnums in descending order from there. When this example is run with the sports database migrated to MS SQL Server, the first record returned has custnum 15, and the repeat loop displays values in descending order from there. This difference in results is a caused by the MAX-ROWS being applied prior to the sorting. Block cursors Block cursors are available as a performance enhancement. They allow blocks of records to be bound and fetched together from a single database request, thus reducing the network overhead and minimizing record copies for ABL queries and finds, and minimizing record copies. Considering block cursors and firehose cursors Block cursors are the default behavior replacing look-ahead cursors for NO-LOCK queries that are processed on the server side. A NO-LOCK query is one that executes with the NO-LOCK lock condition attached to its ABL statement. Block cursors are the preferred choice to process NO-LOCK queries on the server side. However, server-side cursor processing is not the primary choice overall. Firehose cursors, providing optimum performance for NO-LOCK queries, surpasses the benefits of block cursors because they are client-based. For an in depth presentation of firehose cursors, see the “Firehose and Fast Forward-Only Cursors” section on page 4–5. Additional details about block cursor behavior DataServer connections that run at the read uncommitted isolation level will also execute queries that specify the SHARE-LOCK condition as NO-LOCK queries and will also utilize block cursors for their result sets. You can shut off block cursor behavior and revert back to look-ahead cursors for NO-LOCK queries by setting the -Dsrv PRGRS_BLOCK_CURS,0. If you leave block cursors on but wish to turn off the block and/or look-ahead cursor optimizations for a specific query, you can set the QUERY-TUNING option QUERY-TUNING(NO-LOOKAHEAD) on your ABL statement. 2–49
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PROGRESS® 10 OPENEDGE® OpenEdge®
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Contents Preface . . . . . . . . .
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Contents Values of output parameter
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Contents 8. Troubleshooting. . . .
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Tables Contents Table 1-1: DataServ
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Examples Contents Example 3-1: Pass
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Preface This Preface contains the f
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Chapter 5, “Configuring the DataS
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Typographical conventions This manu
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Preface A called external procedure
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Preface Obtaining more information
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Preface Copyright © 1991 by Lucent
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Preface OpenEdge includes Sonic sof
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Preface WARRANTIES, INCLUDING, BUT
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Introduction 1 The OpenEdge® DataS
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DataServer components DataServer co
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DataServer for MS SQL Server logic
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DataServer components If you plan t
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DataServer utilities DataServer uti
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DataServer configurations DataServe
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DataServer configurations Configuri
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Typical configuration scenarios Dat
Page 45 and 46: Guidelines for using the DataServer
Page 47 and 48: Documentation resources Documentati
Page 49 and 50: Initial Programming Considerations
Page 51 and 52: Database design issues Database des
Page 53 and 54: MS SQL Server DataServer data sourc
Page 55 and 56: Database design issues For example,
Page 57 and 58: Support for Unicode Database design
Page 59 and 60: Database design issues restrictions
Page 61 and 62: Database design issues For example,
Page 63 and 64: OpenEdge sequences Database design
Page 65 and 66: Data types MS SQL Server data types
Page 67 and 68: Table 2-5: MS SQL Server data type
Page 69 and 70: Determining your application needs
Page 71 and 72: Data types The ABL DATETIME and DAT
Page 73 and 74: Data types Table 2-10 provides deta
Page 75 and 76: Schema Migration > OpenEdge DB to M
Page 77 and 78: Default and Special Datetime Defaul
Page 79 and 80: Table 2-12 depicts mapping between
Page 81 and 82: Record creation Record creation Rec
Page 83 and 84: Record creation The VALIDATE or REL
Page 85 and 86: Share locks Data source record lock
Page 87 and 88: Additional record locking details D
Page 89 and 90: Data source record locking to be lo
Page 91 and 92: Transactions Transactions With Data
Page 93 and 94: Error handling Error handling One c
Page 95: Overflow checking Error handling Ov
Page 99 and 100: Block cursors on versus off Cursors
Page 101 and 102: ABL issues • If you force the cre
Page 103 and 104: ABL issues Include the SCROLLING op
Page 105 and 106: ABL issues When you run find.p with
Page 107 and 108: NO-LOCK option 1 SHARE-LOCK option
Page 109 and 110: RDBMS Stored Procedure Details 3 Th
Page 111 and 112: RDBMS stored procedure basics RDBMS
Page 113 and 114: RDBMS stored procedure basics schem
Page 115 and 116: Run Stored-Procedure details •
Page 117 and 118: Run Stored-Procedure details An exp
Page 119 and 120: Run Stored-Proc statement execution
Page 121 and 122: Data output and retrieval options D
Page 123 and 124: Interfacing with RDBMS stored proce
Page 125 and 126: Technique to use proc-text-buffer I
Page 129 and 130: Loading result sets into temp-table
Page 133 and 134: Details about a dynamic temp-table
Page 139 and 140: Handling errors • If you try to e
Page 141 and 142: ROWID Support It is important to no
Page 143 and 144: ROWID Support If the table uses com
Page 145 and 146: DEFINE VARIABLE hSendSQL AS HANDLE
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Additional Features to Enhance Data
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Enhancements overview For installat
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Firehose and Fast Forward-Only Curs
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• Lowest connection value • Num
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Query tuning Query tuning How you s
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LOOKAHEAD NO-LOOKAHEAD SEPARATE-CON
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Caching records Caching records The
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Join by SQLDB FOR EACH customer, EA
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Modifying the run-time schema check
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Configuring the DataServer 5 Config
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DataServer components Table 5-1: In
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Configuring a local DataServer Conf
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Configuring a remote DataServer 5.
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Configuring a remote DataServer For
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Configuring a remote DataServer Whe
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Configuring a remote DataServer The
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Creating a schema holder Creating a
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Creating a schema holder 4. Start t
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Creating a schema holder Table 5-4
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Creating a schema holder You can al
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Typical configuration for a remote
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Typical configuration for a remote
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Connecting the DataServer You can s
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Starting a remote DataServer Starti
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Starting a remote DataServer Starti
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Starting a remote DataServer For ex
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Connecting a schema holder Connecti
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Direct Connect (-DirectConnect) Pas
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Note the following command syntax u
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Use the PRGRS_CONNECT parameter in
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Connecting a schema holder Table 6-
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Connecting a schema holder 3. The v
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Connecting a schema holder Note: Ap
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Connecting a schema holder The ABL
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Connection troubleshooting Connecti
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Setting the log file location Conne
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The DataServer Tutorial 7 This chap
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Preparing to create demonstration d
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Preparing to create demonstration d
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DataServer utilities When you acces
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Creating a schema holder 4. In the
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Updating a schema holder Updating a
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Verifying a schema holder Verifying
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Verifying a schema holder 4. There
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Changing connection information in
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Deleting a schema holder Deleting a
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Migrating an OpenEdge database to M
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Delta df to MS SQL Server Increment
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Modifying field-level information Y
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Defining the ROWID Modifying a sche
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Adding extended ABL support Adding
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Adding extended ABL support Using c
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Adding extended ABL support create
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Troubleshooting This chapter descri
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ODBC options Tuning your environmen
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Tuning your environment with the -D
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SVUB,x—the Unified Broker Server
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Adjusting values Tuning your enviro
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Migration Issues A This appendix di
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Modifying your application Note the
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Sample code for the db.owner.Custom
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Server Related Command Line Utiliti
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-validate -help Progress Explorer c
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-host host-name Progress Explorer c
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Progress Explorer command line util
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-user user-name Progress Explorer c
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Syntax Parameters service-name PROB
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Non-Progress Explorer command line
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Data Type Details C This appendix s
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ntext 9 nvarchar(max) SQL_NLONGVARC
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Using qt_debug to Analyze Performan
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Index Numbers 4GLTrans log entry ty
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Data types 2-17, C-1 changing 7-34
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K Key buffer troubleshooting 8-8 Ke
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Progress Explorer Framework 5-23 an
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Service Name (-S) shutdown paramete
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OpenEdge Data Management: DataServer for Microsoft SQL Server

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