Database Administrator's Guide

Server Memory Calculations

The considerations listed on this page apply to the non-SQL version of the FairCom Server.

The FairCom Server startup memory requirements can be reasonably approximated with the following equation:

Base line Memory =

Server EXE size + 1 MB +

Communications Library size (if applicable) +

Data cache (DAT_MEMORY) +

Index buffer (IDX_MEMORY) +

(900 bytes * Number of files (FILES)) +

(325 bytes * Maximum number of connections (CONNECTIONS)) +

(4 bytes * Maximum number of connections (CONNECTIONS)

* Maximum number of connections (CONNECTIONS)) +

(16000 bytes * Number of actual connections) +

(256 bytes per connection per file actually opened)

Note the following points:

• DAT_MEMORY and IDX_MEMORY defaults vary between releases. For details, see the ctsrvr.cfg for your specific release, and the documentation.
  

  IDX_MEMORY <bytes>

  The memory allocated to the index cache, specified in bytes. Within the memory constraints of the hardware, there is no effective limit. High-speed buffer search routines ensure quick access to the entire cache.

  Default: 100 MB

  Note: Prior to V11, the default value for both the standard FairCom DB Server and the FairCom DB SQL Server was 600 * PAGE_SIZE. Assuming a default page size of 8192, the default DAT_MEMORY would be 4915200.

  

  PAGE_SIZE <bytes>

  The number of bytes per buffer page (maximum 65536 bytes). Only the following values are accepted (all other values generate an error):

  • 1024
  • 2048
  • 4096
  • 8192
  • 16384
  • 32768
  • 65536

  To encourage compatibility across different FairCom DB environments, we suggest not modifying the PAGE_SIZE. However, if performance is of concern, this value may be modified to suit the characteristics of the operating system. Generally, this is a matter to discuss with the application programmer.

  Default: 32768 in V12 and later (before V12, the default was 8192)

  Warning: Changing the PAGE_SIZE is a maintenance task that should be done carefully and with a full reliable backup. Practice on a copy of your data and server folder until you are confident with the results. For procedures, see Adjusting PAGE_SIZE in the FairCom Installation Guide.

  Note: A file created with a larger PAGE_SIZE cannot be opened by a server with a smaller PAGE_SIZE.

  See Also

  • BUFR_MEMORY
  • DAT_MEMORY
  • TOT_MEMORY (deprecated - not recommended)
  • USR_MEMORY

  

  DAT_MEMORY <bytes>

  The memory allocated to the data cache, specified in bytes. Within the memory constraints of the hardware, there is no effective limit.

  Default: 100 MB

  Note: Prior to V11, the default value for both the standard FairCom DB Server and the FairCom DB SQL Server was 600 * PAGE_SIZE. Assuming a default page size of 8192, the default DAT_MEMORY would be 4915200.

  See Also

  • BUFR_MEMORY
  • IDX_MEMORY
  • TOT_MEMORY (deprecated - do not use)
  • USR_MEMORY

• PAGE_SIZE has changed by default over the various releases. V10-V11 default to 8K. V12 and later default to 32K.
• FILES defaults to 1000.
  

  FILES <Number of Files>

  The maximum number of files to be open at one time.

  There is no effective limit to the number of files supported by the FairCom Server, except for any limits imposed by the operating system and available system memory.

  Note: The number of file descriptors set by the FILES keyword may need to be considerably greater than the number of open data files. Each index, whether or not in a separate file, counts toward this total. For example, a host index file that supports three different keys (i.e., contains three separate index members) counts as three files toward the FILES total. In addition, each member of a superfile is counted toward the total set by the FILES keyword.

  Unix/Linux Considerations

  The Unix and Linux operating systems place a limit on the number of file descriptors that can be in use at one time. The number of file descriptors required by FairCom DB is determined as follows:

  • Each open file consumes 1 file descriptor (this may be somewhat lower than the setting of the FILES keyword because individual superfile members and members of a host index do not consume file descriptors).
  • Each TCP/IP socket consumes a file descriptor (this corresponds to the CONNECTIONS keyword).
  • FairCom DB reserves a few file descriptors in addition to those used for data files, index files, and TCP/IP connections.

  Based on the above considerations, the system should be configured to allow a number somewhat greater than the number of files + connections.

  The file descriptor limit is typically set by the limit or ulimit command, which may require superuser access, or by the hard limit set in a system configuration file such as /etc/security/limits.conf on Linux. The specifics vary by system, so consult the documentation for your Unix or Linux system. (Unix and Linux define both hard limits and soft limits. A soft limit can be changed by a process at any time, but it cannot exceed the hard limit. The hard limit is of interest for this discussion.)

  Note: When the file descriptor limit for FairCom Server (set by the operating system) is set too low, server startup fails with error 1005 (system-dependent initialization failed). A message is written to standard output indicating that system-dependent initialization failed and that details are in CTSTATUS.FCS.

  Features for Handling File Descriptor Limits

  Several features improve the ability of the system to handle situations concerning file descriptors:

  • Improved file descriptor server startup messages
  • Fail server startup if file descriptor limit can't be increased to required value
  • Write message to standard output when file descriptor limit is too low
  • New file descriptor limit compatibility keyword

  See Also

  MAX_FILES_PER_USER

  COMPATIBILITY FILE_DESCRIPTOR_LIMIT

• CONNECTIONS default to 128.
  

  CONNECTIONS <Number of Connections>

  The maximum number of connections to the FairCom Server. Typically, a FairCom Server is activated to support up to one of the following values for concurrent user connections: 8, 16, 32, 64, 128, 256, 512, or 1024. However, your particular FairCom Server may be customized with a different value for connections. Specifying a number of users greater than the actual number of users needed results in inefficiencies (e.g., unused memory), so the goal is to keep this number as low as feasible on the system. The Activation Key flier displays the allowable number of users for your FairCom Server, as does the FairCom Server startup screen.

  Default: Activated number of connections in the license

• IDX_MEMORY is the MAX of:
  • IDX_MEMORY or
  • 3 * CONNECTIONS * (PAGE_SIZE + 400), where PAGE_SIZE defaults to 8K.

The following locking/transaction processing related items should be considered when approximating the FairCom Server dynamic memory requirements:

• Each record locked consumes 24 bytes.

For transaction processing files only:

• Each data record written consumes (record length + 42) bytes.
• Each index operation consumes (key length + 42) bytes.

Note: Some operating systems offer virtual RAM (VRAM) which swaps data from memory to the hard drive. VRAM is usually automatically invoked if RAM gets full. Since data is being moved to and from the hard drive by VRAM, applications will often slow. If your system suddenly slows, examine this possible cause with your system administrator.