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GEOS SDK TechDocs
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Virtual Memory
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2 VM Structure
The GEOS Virtual Memory file management system is designed to provide features not easily available with standard file systems. Designed primarily for use by applications for long-term data storage, it is also used by the system for many other purposes, such as to provide state saving (in the UI). The main benefits it provides to applications include the following:
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Convenient file structure
GEOS divides VM files into VM blocks, each of which is accessed via a VM block handle. This structure is much like a "disk-based heap," and is analogous to (and compatible with) the memory heap. VM blocks are accessed the same way whether they are on disk or resident in memory. They can be independently resized and locked.
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Ease of file manipulation
Many file manipulation techniques are much simpler with VM files. For example, geodes do not have to keep track of which blocks they have changed; instead, when they change a block, they mark it as dirty, and when they update the file, the virtual memory routines will automatically copy just the changed blocks to the disk.
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Sharing of Data Files
GEOS maintains information about each VM file and knows when more than one thread is using it. This allows the system to notify all users when one thread has modified a file. The system provides data synchronization for individual blocks.
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Integrity of Data Files
GEOS provides several features to protect the integrity of VM files. For example, you can request that GEOS maintain a backup that can be used to restore the file to its last-saved state. In addition, you can have GEOS do all writing to the file synchronously to ensure that all the data in the file stays consistent even if GEOS is somehow interrupted.
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Uniform File Structure
Because all GEOS data files are based on VM files, utilities can be written which work for all VM files. For example, the Document Control objects can take care of opening, closing, and saving all data files which are based on VM files. Furthermore, data structures can be designed which can be added at will into any VM file.
| GEOS SDK TechDocs
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| Virtual Memory
| 2 VM Structure