Chapter 7
Tuning Perforce for Performance

This chapter briefly outlines some of the factors that can affect the performance of a Perforce server, provides a few tips on diagnosing network-related difficulties, and offers some suggestions on decreasing server load for larger installations.

Tuning for performance

Memory

• Determining memory requirements for large queries is fairly straightforward: the server requires about 1 kilobyte of RAM per file to avoid paging; 10,000 files will require 10 MB of RAM.

• To cache db.rev, the size of the db.rev file in an existing installation can be observed and used as an estimate. New installations of Perforce can expect db.rev to require about 150-200 bytes per revision, and roughly three revisions per file, or about 0.5 kilobytes of RAM per file.

For most installations, a system with enough1.5 kilobytes of RAM per file in the depot suffices.

Filesystem performance

The only disk-intensive activity is file check-in, where the Perforce server must write and rename files in the archive. Server performance depends heavily on the operating system's filesystem implementation, and in particular, on whether directory updates are synchronous.

Although Perforce does not recommend any specific filesystem, Linux servers are generally fastest (owing to Linux's asynchronous directory updating), but they may have poor recovery if power is cut at the wrong time. The BSD filesystem (also used in Solaris) is relatively slow but much more reliable. NTFS performance falls somewhere in between these two ranges. The filesystems used by IRIX and OSF have demonstrated an excellent combination of both speed and robustness.

Performance in systems where database and versioned files are stored on NFS-mounted volumes is typically dependent on the implementation of NFS in question or the underlying storage hardware. Perforce has been tested and is supported under the Solaris implementation of NFS.

Under Linux and FreeBSD, database updates over NFS can be an issue because file locking is relatively slow; if the journal is NFS-mounted on these platforms, all operations will be slower. In general (but in particular on Linux and FreeBSD), we recommend that the Perforce database, depot, and journal files be stored on disks local to the machine running the Perforce server process.

These issues affect only the Perforce server process (p4d). Perforce client programs, (such as p4, the Perforce Command-Line Client) have always been able to work with client workspaces on NFS-mounted drives (for instance, workspaces in users' home directories).

Disk space allocation

• Number and size of client workspaces

• Size of server database

• Size of server's archive of all versioned files

The client file space required is the size of the files that your users will need in their client workspaces at any one time.

The server's database size can be calculated with a fair level of accuracy; as a rough estimate, it requires 0.5 kilobytes per user per file. (For instance, a system with 10,000 files and 50 users requires 250 MB of disk space for the database). The database can be expected to grow over time as histories of the individual files grow.

The size of the server's archive of versioned files depends on the sizes of the original files stored and grows as revisions are added. For most sites, allocate space equivalent to at least three times the aggregate size of the original files.

If you anticipate your database growing into the gigabyte range, you should ensure that your platform has adequate support for large filesystems. See "Allocate sufficient disk space for anticipated growth" on page 20.

The db.have file holds the list of files opened in client workspaces. This file tends to grow more rapidly than other files in the database. If you are experiencing issues related to the size of your db.have file and are unable to quickly switch to a server with adequate support for large files, deleting unused client workspace specifications and reducing the scope of client workspace views can help alleviate the problem.

Network

Perforce uses a TCP/IP connection for each client interaction with the server. The server's port address is defined by P4PORT, but the TCP/IP implementation picks a client port number. After the command completes and the connection is closed, the port is left in a state called TIME_WAIT for two minutes. Although the port number ranges from 1025 to 32767, generally only a few hundred or thousand can be in use simultaneously. It is therefore possible to occupy all available ports by invoking a Perforce client command many times in rapid succession, such as with a script.

Before release 99.2, both the server and client side of the connection remained in TIME_WAIT, which meant that a script running on one user's machine could deprive other users of service by tying up all available ports on the server side. As of Release 99.2, only the client side goes into TIME_WAIT, leaving the Perforce server free to handle other clients.

CPU

In general, CPU power is not a major consideration when determining the platform on which to install a Perforce server.

Diagnosing slow response times

1. Misconfigured domain name system (DNS)

2. Misconfigured Windows networking

3. Difficulty accessing the p4 executable on a networked file system

Hostname vs. IP address

P4PORT=host.domain:1666

P4PORT=1.2.3.4:1666

On most systems, you can determine the IP address of a host by invoking:

ping hostname

Try p4 info vs. P4Win

If P4Win returns the information quickly, but p4 info is slow, you have a DNS-related problem. (When the Perforce server receives a p4 info request from either the command line or from P4V, the server performs a reverse name lookup in order to send back both the client and server hostnames along with other configuration information. When the server receives a P4Win"Show Connection Info" request, however, it simply returns the IP addresses.)

Windows wildcards

p4 files //depot/*

p4 files "//depot/*"

DNS lookups and the hosts file

The corresponding UNIX file is /etc/hosts.

Location of the p4 executable

p4 -V

Preventing server swamp

The number of files affected by a single command is largely determined by:

• p4 command-line arguments (or selected folders in the case of GUI operations)

Without arguments, most commands operate on, or at least refer to, all files in the client workspace view.

• Client views, branch views, label views, and protections

Because commands without arguments operate on all files in the workspace view, it follows that the use of unrestricted views and unlimited protections can result in commands operating on all files in the depot.

At sites with very large depots, unrestricted views and unqualified commands make a Perforce server work much harder than it needs to. Users and administrators can ease load on their servers by:

• Using "tight" views

• Assigning protections

• Limiting maxresults

• Writing efficient scripts

• Using compression efficiently

Using tight views

In the loose view, the entire depot was mapped into the client workspace; for most users, this can be "tightened" considerably. The following view, for example, is restricted to specific areas of the depot:

Client views, in particular, but also branch views and label views, should also be set up to give users just enough scope to do the work they need to do.

Client, branch, and label views are set by a Perforce administrator or by individual users with the p4 client, p4 branch, and p4 label commands, respectively.

Two of the techniques for script optimization (described in "Using branch views" on page 125 and "The temporary client workspace trick" on page 126) rely on similar techniques. By limiting the size of the view available to a command, fewer commands need to be run, and when run, the commands require fewer resources.

Assigning protections

Unlike client, branch, and label views, however, the views used by protections can be set only by Perforce superusers. (Protections also control read and write permission to depot files, but the permission levels themselves have no impact on server performance.) By assigning protections in Perforce, a Perforce superuser can effectively limit the size of a user's view, even if the user is using "loose" client specifications.

Protections can be assigned to either users or groups. For example:

Perforce groups are created by superusers with the p4 group command. Not only do they make it easier to assign protections, they also provide useful fail-safe mechanisms in the form of maxresults and maxscanrows, described in the next section.

Limiting database queries

Users in such groups are unable to run any commands that affect more database rows than the group's maxresults limit. (For most commands, the number of database rows affected is roughly equal to the number of files affected.)

Like maxresults, maxscanrows prevents certain user commands from placing excessive demands on the server. (For most commands, the number of rows that could be scanned is roughly equal to the number of files affected, multiplied by the average number of revisions per file in the depot.)

To set these limits, fill in the Maxresults: or Maxscanrows: field in the p4 group form. If a user is listed in multiple groups, the highest of the maxresults (or maxscanrows) limits (but not including the default unlimited setting) for those groups is taken as the user's maxresults (or maxscanrows) value.

Example:  Effect of setting maxresults and maxscanrows

As an administrator, you want members of the group rocketdev to be limited to operations of 20,000 files or less, and that scan no more than 100,000 revisions:

Group:        rocketdev Maxresults:   20000 Maxscanrows:  100000 Timeout:      43200 Subgroups: Users:                 bill         ruth         sandy

Suppose that Ruth has an unrestricted ("loose") client view. She types:

p4 sync

Her sync command is rejected if the depot contains more than 20,000 files. She can work around this limitation either by restricting her client view, or, if she needs all of the files in the view, by syncing smaller sets of files at a time, as follows:

p4 sync //depot/projA/...
p4 sync //depot/projB/...

Either method enables her to sync her files to her workspace, but without tying up the server to process a single extremely large command.

Ruth tries a command that scans every revision of every file, such as:

p4 filelog //depot/projA/...

If there are fewer than 20,000 files, but more than 100,000 revisions (perhaps the projA directory contains 8000 files, each of which has 20 revisions), the maxresults limit does not apply, but the maxscanrows limit does.

To remove any limits on the number of result lines processed (or database rows scanned) for a particular group, set the Maxresults: or Maxscanrows: value for that group to unlimited.

Because these limitations can make life difficult for your users, do not use them unless you find that certain operations are slowing down your server. The Maxresults: value should never be less than 10,000, because certain operations performed by P4Win, the Perforce Windows Client, can require a Maxresults: value between 5,000 and 8,000. Similarly, Maxscanrows should rarely need to be set below 50,000.

For more information, including a comparison of Perforce commands and the number of files they affect, type:

p4 help maxresults
p4 help maxscanrows

Maxresults and maxscanrows for users in multiple groups

A side effect of this is that you can't create a group that assigns unlimited values to superusers, because if any of the users in such a group were to belong to another group, the unlimited limit from the superuser group would also apply to them. You can get around this by assigning a very high maxresults limit to your superusers group.

For example:

(The largest possible maxresults or maxscanrows limit is platform-dependent; on most platforms, this is a 32-bit integer.)

Scripting efficiently

This section points out some common efficiency problems and solutions.

Iterating through files

To this end, scripts should never iterate through files running Perforce commands when they can accomplish the same thing by running one Perforce command on a list of files and iterating through the command results.

For example, try a more efficient approach like this:

for i in `p4 diff2 path1/... path2/...`
do
    [process diff output]
done

for i in `p4 files path1/...`
do
    p4 diff2 path1/$i path2/$i
    [process diff output]
done

Using list input files

For example, if your script might look something like this:

for components in header1 header2 header3
do
    p4 edit ${component}.h
done

for components in header1 header2 header3
do
    echo ${component}.h >> LISTFILE
done
p4 -x LISTFILE edit

Using branch views

p4 diff2 pathA/src/...   pathB/src/...
p4 diff2 pathA/tests/... pathB/tests/...
p4 diff2 pathA/doc/...   pathB/doc/...

...and replacing the three commands with one:

p4 diff2 -b pathA-pathB

Limiting label references

For example, this:

p4 files path/...@label | egrep "path/f1.h|path/f2.h|path/f3.h"

p4 files path/f1.h@label path/f1.h@label path/f3.h@label

p4 files path/f1.h@label
p4 files path/f2.h@label
p4 files path/f3.h@label

The temporary client workspace trick

For instance, suppose your script runs these commands:

p4 sync pathA/src/...@label
p4 sync pathB/tests/...@label
p4 sync pathC/doc/...@label

Using this workspace specification, you can then run:

p4 -c XY-temp sync @label

Using compression efficiently

Some file formats (for example, .GIF and .JPG images, .MPG and .AVI media content, files compressed with .gz and .ZIP compression) include compression as part of the file format. Attempting to compress such files on the Perforce server results in the consumption of server CPU resources with little or no savings in disk space.

To disable server storage compression for these file types, specify such files as type binary+F (binary, stored on the server in full, without compression) either from the command line or from the p4 typemap table.

For more about p4 typemap, including a sample typemap table, see "Defining filetypes with p4 typemap" on page 48.

Checkpoints for database tree rebalancing

Eventually, the tree can become sufficiently unbalanced that performance is negatively affected. The Perforce checkpoint and restore processes (see "Backup and recovery concepts" on page 25) re-create the trees in a balanced manner, and consequently, you might see some increase in server performance following a backup, a removal of the db.* files, and the re-creation of the db.* files from a checkpoint.

Rebalancing the trees is normally useful only if the database files have become more than about 10 times the size of the checkpoint. Given the length of time required for the trees to become unbalanced during normal Perforce use, we expect that the majority of sites will never need to restore the database from a checkpoint (that is, rebalance the trees) for performance reasons.