Stata 15 help for maxvar

[D] memory -- Memory management

Syntax

Display memory usage report

memory

Display memory settings

query memory

Modify memory settings

set maxvar # [, permanently]

set niceness # [, permanently]

set min_memory amt [, permanently]

set max_memory amt [, permanently]

set segmentsize amt [, permanently]

where amt is #[b|k|m|g], and the default unit is b.

+-------------------------------------------------------+ | Parameter | Default | Minimum Maximum | |-------------+---------+-------------------------------| | maxvar | 5000 | 2048 120000 | (MP) | | 5000 | 2048 32767 | (SE) | | 2048 | 2048 2048 | (IC) | | | | | niceness | 5 | 0 10 | | | | | | min_memory | 0 | 0 max_memory | | max_memory | . | 2*segmentsize . | | segmentsize | 32m | 1m 32g | (64-bit) | | 16m | 1m 1g | (32-bit) +-------------------------------------------------------+

Notes:

1. The maximum number of variables in your dataset is limited to maxvar. The default value of maxvar is 5,000 for Stata/MP and Stata/SE, and 2,048 for Stata/IC. With Stata/MP and Stata/SE, this default value may be increased by using set maxvar. The default value is fixed for Stata/IC.

2. Most users do not need to read beyond this point. Stata's memory management is completely automatic. If, however, you are using the Linux operating system, see Serious bug in Linux OS under Remarks below.

3. The maximum number of observations is fixed at 1,099,511,627,775 for Stata/MP and is fixed at 2,147,483,647 for Stata/SE and Stata/IC regardless of computer size or memory settings. Depending on the amount of memory on your computer, you may face a lower practical limit. See help obs_advice.

4. max_memory specifies the maximum amount of memory Stata can use to store your data. The default of missing (.) means all the memory the operating system is willing to supply. There are three reasons to change the value from missing to a finite number.

1. You are a Linux user; see Serious bug in Linux OS under Remarks below.

2. You wish to reduce the chances of accidents, such as typing expand 100000 with a large dataset in memory and actually having Stata do it. You would rather see an insufficient-memory error message. Set max_memory to the amount of physical memory on your computer or more than that if you are willing to use virtual memory.

3. You are a system administrator; see Notes for system administrators under Remarks below.

5. The remaining memory parameters -- niceness, min_memory, and segment_size -- affect efficiency only; they do not affect the size of datasets you can analyze.

6. Memory amounts for min_memory, max_memory, and segmentsize may be specified in bytes, kilobytes, megabytes, or gigabytes; suffix b, k, m, or g to the end of the number. The following are equivalent ways of specifying 1 gigabyte:

1073741824 1048576k 1024m 1g

Suffix k is defined as (multiply by) 1024, m is defined as 1024^2, and g is defined as 1024^3.

7. 64-bit computers can theoretically provide up to 18,446,744,073,709,551,616 bytes of memory, equivalent to 17,179,869,184 gigabytes, 16,777,216 terabytes, 16,384 petabytes, or 16 exabytes. Real computers have less.

8. 32-bit computers can theoretically provide up to 4,294,967,296 bytes of memory, equivalent to 4,194,304 kilobytes, 4,096 megabytes, or 4 gigabytes. Most 32-bit operating systems limit Stata to half that.

9. Stata allocates memory for data in units of segmentsize. Smaller values of segmentsize can result in more efficient use of available memory but require Stata to jump around more. The default provides a good balance. We recommend resetting segmentsize only if your computer has large amounts of memory.

10. If you have large amounts of memory and you use it to process large datasets, you may wish to increase segmentsize. Suggested values are

memory segmentsize ------------------------ 32g 64m 64g 128m 128g 256m 256g 512m 512g 1g 1024g 2g ------------------------

11. niceness affects how soon Stata gives back unused segments to the operating system. If Stata releases them too soon, it often needs to turn around and get them right back. If Stata waits too long, Stata is consuming memory that it is not using. One reason to give memory back is to be nice to other users on multiuser systems or to be nice to yourself if you are running other processes.

The default value of 5 is defined to provide good performance. Waiting times are currently defined as

niceness waiting time (m:s) --------------------------------- 10 0:00.000 9 0:00.125 8 0:00.500 7 0:01 6 0:30 5 1:00 4 5:00 3 10:00 2 15:00 1 20:00 0 30:00 ---------------------------------

Niceness 10 corresponds to being totally nice. Niceness 0 corresponds to being an inconsiderate, self-centered, totally selfish jerk.

12. min_memory specifies an amount of memory Stata will not fall below. For instance, you have a long do-file. You know that late in the do-file, you will need 8 gigabytes. You want to ensure that the memory will be available later. At the start of your do-file, you set min_memory 8g.

13. Concerning min_memory and max_memory, be aware that Stata allocates memory in segmentsize blocks. Both min_memory and max_memory are rounded down. Thus the actual minimum memory Stata will reserve will be segmentsize*trunc(min_memory/segmentsize). The effective maximum memory is calculated similarly. (Stata does not round up min_memory because some users set min_memory equal to max_memory.)

Description

Memory usage and settings are described here.

memory displays a report on Stata's current memory usage.

query memory displays the current values of Stata's memory settings.

set maxvar, set niceness, set min_memory, set max_memory, and set segmentsize change the values of the memory settings.

If you are a Unix user, see Serious bug in Linux OS under Remarks below.

Options

permanently specifies that, in addition to making the change right now, the new limit be remembered and become the default setting when you invoke Stata.

once is not shown in the syntax diagram but is allowed with set niceness, set min_memory, set max_memory, and set segmentsize. It is for use by system administrators; see Notes for system administrators under Remarks below.

Remarks

Remarks are presented under the following headings:

Examples Serious bug in Linux OS Notes for system administrators

Examples

Obtain memory-usage report . memory

Obtain current memory-settings report . query memory

Reset maximum number of allowed variables . set maxvar 5000

Reset memory settings . set max_memory 32g . set min_memory 8g . set max_memory . . set min_memory 0

Serious bug in Linux OS

If you use Linux OS, we strongly suggest that you set max_memory. Here's why:

"By default, Linux follows an optimistic memory allocation strategy. This means that when malloc() returns non-NULL there is no guarantee that the memory really is available. This is a really bad bug. In case it turns out that the system is out of memory, one or more processes will be killed by the infamous OOM killer. In case Linux is employed under circumstances where it would be less desirable to suddenly lose some randomly picked processes, and moreover the kernel version is sufficiently recent, one can switch off this overcommitting behavior using [...]" -- Output from Unix command man malloc.

What this means is that Stata requests memory from Linux, Linux says yes, and then later when Stata uses that memory, the memory might not be available and Linux crashes Stata, or worse. The Linux documentation writer exercised admirable restraint. This bug can cause Linux itself to crash. It is easy.

The proponents of this behavior call it "optimistic memory allocation". We will, like the documentation writer, refer to it as a bug.

The bug is fixable. Type man malloc at the Unix prompt for instructions. Note that man malloc is an instruction of Unix, not Stata. If the bug is not mentioned, perhaps it has been fixed. Before assuming that, we suggest using a search engine to search for "linux optimistic memory allocation".

Alternatively, Stata can live with the bug if you set max_memory. Find out how much physical memory is on your computer and set max_memory to that. If you want to use virtual memory, you might set it larger, just make sure your Linux system can provide the requested memory. Specify the option permanently so you only need to do this once. For example,

. set max_memory 16g, permanently

Doing this does not guarantee that the bug does not bite, but it makes it unlikely.

Notes for system administrators

System administrators can set max_memory, min_memory, and niceness so that Stata users cannot change them. You may want to do this on shared computers to prevent individual users from hogging resources.

There is no reason you would want to do this on users' personal computers.

You can also set segmentsize, but there is no reason to do this even on shared systems.

The instructions are to create (or edit) the text file sysprofile.do in the directory where the Stata executable resides. Add the lines

set min_memory 0, once set max_memory 16g, once set niceness 5, once

The file must be plain text, and there must be end-of-line characters at the end of each line, including the last line. Blank lines at the end are recommended.

The 16g on set max_memory is merely for example. Choose an appropriate number.

The values of 0 for min_memory and 5 for niceness are recommended.

Stored results

memory stores all reported numbers in r(). StataCorp may change what memory reports, and you should not expect the same r() results to exist in future versions of Stata. To see the stored results from memory, type return list, all.


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