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FairCom ISAM for C

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I/O Management

The following file modes are related to I/O management:

  • ctDUPCHANNEL
  • ctWRITETHRU

With the FairCom DB Server you can control how the Server uses I/O channels. This mode is discussed in FairCom DB Server Server.

ctWRITETHRU forces the operating system to flush all disk cache buffers when a data write occurs. This parameter can slow performance of the file handler. On the other hand, it is an important feature to use if you want to ensure that all data writes are put to the disk immediately. It is particularly important if you are in an operating environment where the system crashes a lot, and you are not using transactions and the ctTRNLOG mode. However, ctWRITETHRU does not guarantee that operating system buffers have been flushed.

Do not use ctWRITETHRU if automatic recovery is active for the file. Writes may be forced to disk on pre-imaged files. The ctWRITETHRU file mode is ignored for ctTRNLOG files, but ctPREIMG files do not ignore the ctWRITETHRU file mode allowing developers to force writes to disk while maintaining atomicity with ctPREIMG. Indexes are placed into standard ctWRITETHRU mode except that changes in the number of index entries are not written to disk until the commit. Data files are placed into a modified mode in which file updates and header updates are only output at commit.

The FairCom DB Server can automatically force ctWRITETHRU on all files not protected with transaction control. See the COMPATIBILITY FORCE_WRITETHRU keyword in the FairCom DB Server Administrator’s Guide and in Migrating Your Application Between Operational Models in this guide.

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