Software Vault: The Gold Collection

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PRODUCT : Paradox NUMBER : 1216 VERSION : 4.0 OS : DOS DATE : January 6, 1993 PAGE : 1/7 TITLE : Understanding and Optimizing Memory in Paradox 4.0 The purpose of this Technical Information Sheet is to develop an understanding of how Paradox uses memory and to acquaint the reader with the tools available for optimizing memory in Paradox 4.0. Memory requirements and recommendations: Paradox can use extended memory for all memory needs and expanded memory as a swap area for data. Paradox 4.0 requires two megabytes of memory to run consistently, however a minimum of four megabytes is recommended for better performance. Paradox can use up to a maximum of 16 megabytes. The error messages "Insufficient Stack Space" and "DPMI Initialization Error" can mean there is too little memory available for Paradox to load. In these cases, sometimes merely reconfiguring how system memory is used can bypass this problem, otherwise eliminating programs and drivers that are competing with Paradox for memory resources and/or adding more memory to the system are indicated. See the section below on the Paradox Memory Environment for further discussion of competing programs and drivers. The minimum XMS requirement for Paradox 4.0 to load is 384 K. The amount of XMS available can be determined with the MEM command in DOS. Systems with more than 16 megabytes of extended RAM must limit Paradox to 16 megabytes with the DOS setting "SET DPMIMEM=MAXMEM 16384" or the "-extk 16384" Paradox command line switch. The DPMIMEM setting tells the Paradox DPMI Server to allow Paradox access to only the specified amount of extended memory. Memory differences between versions 3.5 and 4.0: Several changes were made in the way Paradox 4.0 utilizes memory. Paradox 3.5 runs in protected or real mode. Version 4.0 runs only in protected mode. Paradox 4.0 is the first version of Paradox to use the DPMI (DOS Protected Mode Interface) memory standard. Using the DPMI standard allows Paradox 4.0 to run in protected mode in Microsoft Windows Enhanced mode, thereby enabling PXACCESS and SQL Link in that environment. DPMI compliance allows Paradox 4.0 to use extended memory above 640 K in Microsoft Windows Enhanced Mode and under OS/2, which can greatly improve performance. PRODUCT : Paradox NUMBER : 1216 VERSION : 4.0 OS : DOS DATE : January 6, 1993 PAGE : 2/7 TITLE : Understanding and Optimizing Memory in Paradox 4.0 Paradox 4.0 internally allocates available memory differently than previous versions. The data cache is now an object cache, which stores forms, reports, and validity files, thus saving disk reads when these objects are called repeatedly in a Paradox session. Data is no longer stored in the cache. Data caching is now provided in the larger Table Buffer area. In Paradox 3.5 the default table buffer is around 100 K. Paradox 4.0 allocates up to 70% of available memory to the table buffer which can mean several megabytes allocated on systems with four or more megabytes of extended memory. How Paradox loads in memory: An explanation of Paradox loading procedure might be helpful in understanding the optimization techniques discussed later. The diagram below and discussion on the following pages describe where and in what order Paradox loads its various components into memory. ┌───────────────────────┐ 16 MB Limit │ Code Pool │ │ 200-1200 K │ ├───────────────────────┤ │ "Heap" │ ├───────────────────────┤ │ Protected-Mode │ │ Resident Block │ ╞═══════════════════════╡ 1024 K │ (Upper Memory) │ ╞═══════════════════════╡ 640 K │ "Real Heap" │ ├───────────────────────┤ │ Real Resident Block │ ├───────────────────────┤ └───────────────────────┘ PRODUCT : Paradox NUMBER : 1216 VERSION : 4.0 OS : DOS DATE : January 6, 1993 PAGE : 3/7 TITLE : Understanding and Optimizing Memory in Paradox 4.0 Overview of memory areas The Protected Mode Resident Block: This houses fixed size program and data segments along with some DPMI server code. What is loaded here must remain throughout the Paradox session. It is usually 300 K to 350 K in size and is not adjustable by the user. The Paradox Code Pool: Here, overlay code segments are loaded. 500 K is considered to be the optimum minimum in 4.0, depending on the amount of RAM available while 1200 K is the maximum. The Code Pool is adjustable with the -codepool xxxx command line switch. Real Mode Resident Blocks: Here some DPMI server code is loaded along with some Paradox code segments needed for real mode operation. What is loaded here must stay in memory for the duration of the Paradox session. The "Heap": All remaining available extended memory and real memory combined is referred to as the Heap. The Heap is in turn allocated to Table Buffer and Central Memory Pool as listed below. The Table Buffer: The Table Buffer is adjustable directly with the -tablek xxxx command line switch. It holds current data records and memo fields during viewing, editing, querying and reporting on tables. Roughly 70% of the Heap is allocated here. The Central Memory Pool (CMP): The Central Memory Pool is adjustable inversely with the -tablek xxxx command line switch. It holds PAL variables, scripts, images, and active forms and reports. Roughly 30% of the Heap is allocated here. Tools for optimizing memory: Among the tools for optimizing memory in Paradox 4.0 are various command line arguments. They are listed on the following pages along with their functions, syntax and applications toward memory optimization. PRODUCT : Paradox NUMBER : 1216 VERSION : 4.0 OS : DOS DATE : January 6, 1993 PAGE : 4/7 TITLE : Understanding and Optimizing Memory in Paradox 4.0 -space: This argument causes Paradox to message several memory allocation figures on the status line upon starting the program. These figures are useful for gaining an understanding of how Paradox is internally allocating memory and for monitoring changes made to those allocations. Paradox -space ktot - the total amount of RAM available to Paradox for operations after the Paradox code itself has loaded. This figure can be used to indicate whether or not the expected amount of memory on the system is indeed being recognized by and is accessible to Paradox. kswap - the amount of RAM allocated to the table buffer and therefore available for data caching. This is an important figure because it is allocated a large portion of available memory by default. It is adjustable with the -tablek switch below. kgetm - the amount of memory allocated to the Central Memory Pool (CMP). This memory is used for caching scripts, procedures, arrays, and variables. Kgetm is adjusted higher by setting the -tablek switch lower. kpool - the amount of memory allocated to the code pool. This is the RAM that caches Paradox code. It may be necessary to set this parameter with the -codepool switch to be a minimum of 500 up to a maximum of 1200. PRODUCT : Paradox NUMBER : 1216 VERSION : 4.0 OS : DOS DATE : January 6, 1993 PAGE : 5/7 TITLE : Understanding and Optimizing Memory in Paradox 4.0 -tablek: This argument sets the amount of RAM to go to the table buffer and is reflected by kswap above. The syntax is "-tablek xxxx", xxxx being an amount of RAM expressed kilobytes. For example: Paradox -tablek 2048 Sets table buffers at 2 megabytes. Setting this parameter higher allows for a larger data cache but at the same time limits the Central Memory Pool. This setting should be set higher in cases where the majority of the memory needs are data related, and lower if the on systems that are going to be scripts and procedure intensive. -codepool: This argument sets the amount of RAM that is allocated to the codepool and is reflected in kpool above. The syntax is "-codepool xxxx", xxxx being an amount of RAM expressed in kilobytes. The command Paradox -codepool 1100 sets the code pool at 1100 kilobytes. The higher the setting, the more Paradox code will be in memory at one time, having a beneficial effect on performance. The minimum recommended setting is 500 K and the maximum Paradox will allocate is 1200 K. -extk: This argument limits Paradox to a given amount of extended RAM. The syntax is "-extk xxxx", xxxx being an amount of RAM expressed in kilobytes. This switch is useful in situations where it is not desirable for Paradox to take control of all available extended memory, under Microsoft Windows for example. It is also used to limit Paradox from attempting to control more than 16 megabytes of RAM, as in: Paradox -extk 16384 PRODUCT : Paradox NUMBER : 1216 VERSION : 4.0 OS : DOS DATE : January 6, 1993 PAGE : 6/7 TITLE : Understanding and Optimizing Memory in Paradox 4.0 -emk: This argument limits Paradox to a given amount of expanded RAM. Paradox -emk 0 keeps Paradox from using any expanded RAM during the session. This can be useful for avoiding conflicts in upper memory between Paradox and other programs or drivers. -cachek: This argument limits the amount of RAM available to the Paradox internal object cache. The cache will be sized dynamically if this switch is not used. -stack: This argument allocates the amount of memory allocated to the internal procedure stack, which keeps track of currently active PAL procedures in memory. The syntax is -stack xx, xx being an amount of RAM up to 64 kilobytes. -norealheap: This argument tells Paradox not to incorporate any leftover real memory into the heap after it has loaded. (See the diagram on page 2). This is to allow or other programs to run concurrently that need real memory to get started. If Quattro Pro can't load from PXACCESS it could be lacking real memory at startup. In this case, the -norealheap switch could be the remedy. The Paradox Memory Environment Disk Caches and RAM Drives: The environment in which Paradox is running is also important to Paradox memory optimization. Disk caching programs can be very useful for avoiding excessive disk access. But, because these programs take a portion of memory "off the top", they can, in modest memory situations (systems with less than four megabytes of extended RAM), severely impede Paradox performance or possibly prevent Paradox from loading at all due to lack of memory. If Paradox seems slow or has problems starting or running out of memory, check to see if a disk cache is loading in the AUTOEXEC.BAT or CONFIG.SYS and, if so, try PRODUCT : Paradox NUMBER : 1216 VERSION : 4.0 OS : DOS DATE : January 6, 1993 PAGE : 7/7 TITLE : Understanding and Optimizing Memory in Paradox 4.0 limiting the RAM available to it. For the same reasons, RAM Disk programs can also cause memory shortages for Paradox and can be adjusted the same way if memory shortages occur. Memory Managers: Paradox can run efficiently with other memory managers. Some of the popular ones, QEMM, 386MAX, and EMM386 are VCPI compliant programs and as such, have a certain effect on how Paradox behaves. When Paradox encounters a VCPI memory manager, it is able to gain control of the memory over which the memory manager itself has control. However the remaining memory, the "unallocated extended memory" is not available to Paradox. For this reason, care should be given when allocating only a portion of memory to one of these memory managers. It might be better for Paradox performance to allocate all or none. Suppose a system has eight megabytes of Extended RAM and is using QEMM as its memory manager and is allocating two megabytes to expanded memory with the parameter "RAM 2048". Paradox will only be able to use those two megabytes but the remaining six megabytes of unallocated extended memory will be lost to Paradox. This could severely impede Paradox performance. For additional information on memory related issues, please see Chapter 23, 'Advanced Topics', in the Paradox 4.0 User's Guide. DISCLAIMER: You have the right to use this technical information subject to the terms of the No-Nonsense License Statement that you received with the Borland product to which this information pertains.