> For the complete documentation index, see [llms.txt](https://docs.videc.de/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://docs.videc.de/acron-9.3/en/anlagenverwaltung/register-datenbank/sonstiges.md).
# Other
## Suppress Database Engine restart
The Database Engine is not started along with the Simulator or Reporter.
The Database Engine is run on a server, so that data can be administered centrally. If the Database Engine is not running when the Reporter starts up, this will prevent it from being started unintentionally on a wrong computer.
## Difference time for data search in hours
This parameter is of importance particularly when importing historical data into the ACRON system and using count value compression or integral compression. The value entered here (max. 8760 hours) relates only to auto variables. For manual variables, the search is automatically extended one year back.
In count value compression, ACRON forms the difference between the current meter reading and the previous reading. When interfacing with external stations it may occur that values are transmitted to ACRON only once a day via the historical data interface to meter. In order to find the previous count value, ACRON must then search back at least one day.
With this parameter you specify the number of hours you want ACRON to search back when detecting count value differences. If the parameter is set too high, it has only a minor impact on performance. If the parameter is set too low, a count value difference may in some circumstances not be formed. If the data from the external station arrive only once a day, you should enter 48 hours in this field to be certain.
## Compress data up to
Setting how far into the future the Database Engine compresses data.
* Current time
The Database Engine always compresses data up to the current time.
* End of day
If process data with future time stamps have been imported into the ACRON database, data compression is carried out up to the last time stamp, but no later than the end of the current day.
## Delete data after n days
Number of days after which the data tables are to be removed.
If you leave this field blank, the data will be kept.
{% hint style="info" %}
Attention
If you do not have appropriate plant backup, the data will be irrevocably lost after the time entered.
{% endhint %}
## Block data transfer
The Database Engine responsible for sorting incoming data into the ACRON database rejects the import of data with a warning if the data is older than the configured number of days.
Such data occurs, for example, when historical data is read in via the Provider, or when corresponding manual values are recorded.
## Percentile value 1, Percentile value 2
Default values for plants as from ACRON version 5.02 are Percentile value 15 and Percentile value 85. For converted plants (from version 4.54 to 6.0) the defaults are Percentile value 50 and Percentile value 90.
## Select compression data
Selection in case of [substitute value formation](/acron-9.3/en/acron_der_anlagenchronist/ersatzwerte.md);
Note
Substitute values are always formed when the value of a process variable moves out of the measuring range and the following ranges are configured for overwritten base values: Interval values, daily values, monthly values, annual values.
* Interval values from n% of overwritten base values
If the percentage of overwritten base values in the base data exceeds the entered value, the associated compression data are marked accordingly.
* Daily values from n% of overwritten base values
If the percentage of overwritten base values in the base data exceeds the entered value, the associated compression data are marked accordingly.
* Monthly values from n% of overwritten base values
If the percentage of overwritten base values in the base data exceeds the entered value, the associated compression data are marked accordingly.
* Annual values from n% of overwritten base values
If the percentage of overwritten base values in the base data exceeds the entered value, the associated compression data are marked accordingly.
## File compression
Windows offers the option to store files or directories in compressed form. Access to the data is then a little slower, but the required hard disk space is roughly halved. If you select this option, the Database Engine automatically activates file compression for ACRON files of a certain age. Performance when accessing the more recent data which are used frequently is then retained in full, while access to the older data becomes somewhat slower.
If this field is left blank, files are not compressed.
## Automatically defragment files in the data/compression path
A fragmented hard disk can have a significant negative impact on system performance. If higher-level mechanisms do not regularly defragment the hard disks, the Database Engine can initiate it.
Note
You are recommended to disable this option for a solid state drive (SSD).
Defragmenting may impair the performance of virtual machines or special hard disk systems. Be sure to follow the manufacturer's instructions.
For an annual report, the hard disk must hold all the data from the entire year. The hard disk drive must have enough available memory for this. The requirement of the hard disk drive is comprised of the following components:
**Maximum hard disk requirement per year in the plant path in Megabytes (MB)**
*Measurement data*
Maximum yearly space = NEXT \* NINT \* 0.004 MB
| | |
| ---- | -------------------------------------------------------------------------- |
| NEXT | Number of defined external variables |
| NINT | Average number of values per day (e.g. 96 with recording every 15 minutes) |
*Data for Service*
Maximum yearly space = number of variables for Service \* 0.1 MB
*Malfunction and message data*
Maximum yearly space in MB = NM / 2000 + NE / 2000
| | |
| -- | ---------------------- |
| NM | Number of malfunctions |
| NE | Number of messages |
**Maximum hard disk requirement per year in the compression path in megabytes (MB):**
*Measurement data*
Maximum yearly space = PV \* (NINT1 + NINT2) \* 0.07 MB
| | |
| ----- | ------------------------------------------------------------------------- |
| NINT1 | Number of primary intervals per day (e.g. 12 with two-hourly compression) |
| NINT2 | Number of secondary intervals per day |
| PV | Number of defined process variables |
---
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