Tuning Perforce for Performance
Your Perforce server should normally be a light consumer of system resources. As your installation grows, however, you might want to revisit your system configuration to ensure that it is configured for optimal 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
In general, Perforce performs well on any server-class hardware platform. The following variables can affect the performance of your Perforce server.
Memory
Server performance is highly dependent upon having sufficient
memory. Two bottlenecks are relevant. The first bottleneck can be
avoided by ensuring that the server doesn't page when it runs large
queries, and the second by ensuring that the
db.rev
table (or at least as much of it as
practical) can be cached in main 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 thedb.rev
file in an existing installation can be observed and used as an estimate. New installations of Perforce can expectdb.rev
to require about 150-200 bytes per revision, and roughly three revisions per file, or about 0.5 kilobytes of RAM per file.
Thus, if there is 1.5 kilobytes of RAM available per file, or 150 MB for 100,000 files, the server does not page, even when performing operations involving all files. It is still possible that multiple large operations can be performed simultaneously and thus require more memory to avoid paging. On the other hand, the vast majority of operations involve only a small subset of files.
For most installations, a system with 1.5 kilobytes of RAM per file in the depot suffices.
Filesystem performance
Perforce is judicious with regards to its use of disk I/O; its metadata is well-keyed, and accesses are mostly sequential scans of limited subsets of the data. The most 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. Server performance is also highly dependent upon the capabilities of the underlying hardware's I/O subsystem.
Although Perforce does not recommend any specific hardware configuration or 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.
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 applications, (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
Perforce disk space usage is a function of three variables:
-
Number and size of client workspaces
-
Size of server database
-
Size of server's archive of all versioned files
All three variables depend on the nature of your data and how heavily you use Perforce.
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.
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.
Monitoring disk space usage
Use the p4 diskspace command to monitor diskspace usage. By default, p4 diskspace displays the amount of free space, diskspace used, and total capacity of any filesystem used by Perforce.
By default, the Perforce Server rejects commands when free space on
the filesystems housing the P4ROOT
,
P4JOURNAL
, P4LOG
, or
TEMP
fall below 10 megabytes. To change this
behavior, set the filesys.P4ROOT.min
(and
corresponding) configurables to your desired limits:
Configurable |
Default Value |
Meaning |
---|---|---|
|
10M |
Minimum diskspace required on server root filesystem before server rejects commands. |
|
10M |
Minimum diskspace required on server journal filesystem before server rejects commands. |
|
10M |
Minimum diskspace required on server log filesystem before server rejects commands. |
|
10M |
Minimum diskspace required for temporary operations before server rejects commands. |
|
10M |
Minimum diskspace required for any depot before server
rejects commands. (If there is less than
|
If the user account that runs the Perforce Server process is
subject to disk quotas, the Server observes these quotas with
respect to the filesys.*.min
configurables,
regardless of how much physical free space remains on the
filesystem(s) in question.
To estimate much disk space is currently occupied by specific files in a depot, use the p4 sizes command with a block size corresponding to that used by your storage solution. For example, the command:
p4 sizes -a -s -b 512 //depot/...
shows the sum (-s
) of all revisions
(-a
) in //depot/...
, as
calculated with a block size of 512 bytes.
//depot/... 34161 files 277439099 bytes 5429111 blocks
The data reported by p4 sizes actually reflects the diskspace required when files are synced to a client workspace, but can provide a useful estimate of server-side diskspace consumption.
Network
Perforce can run over any TCP/IP network. Although we have not yet seen network limitations, the more bandwidth the better.
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 command many times in
rapid succession, such as with a script.
By default, idle connections are not kept alive. If your network silently drops idle connections, this behavior may cause unexpected connectivity issues. (Consider a p4 pull thread that transfers data between a master server and a replica at a remote site; depending on each site's respective business hours and user workloads, such a connection could be idle for several hours per day.) Four configurables are available to manage the state of idle connections.
Configurable |
Default Value |
Meaning |
---|---|---|
|
0 |
If non-zero, disable the sending of TCP keepalive packets. |
|
0 |
Idle time (in seconds) before starting to send keepalives. |
|
0 |
Interval (in seconds) between sending keepalive packets |
|
0 |
Number of unacknowledged keepalives before failure |
If your network configuration requires keepalive packets, consider
setting net.keepalive.idle
to a suitably long
value, for example 3600 seconds (1 hour), and an interval measured
in tens of minutes.
CPU
The Perforce versioning service is relatively lightweight in terms of CPU resource consumption; in general, CPU power is not a major consideration when determining the platform on which to install a Perforce server.
Improving concurrency with lockless reads
Prior to Release 2013.3, commands that only read data from the database take a read-lock on one (or more) database tables. Although other commands can read from the tables at the same time, any commands attempting to write to the read-locked tables are forced to wait for the read-lock to complete before writing could commence.
The 2013.3 release of the Perforce Server provides some commands with the ability to perform lock-free reads (or "peeks") on these these tables, without sacrificing consistency or isolation. This new behavior ensures that write operations on these tables are able to run immediately, rather than being held until the read-lock is released.
The performance improvement provided by enabling lockless reads can be substantial.
Enabling lockless reads (db.peeking)
To enable lockless reads on your Perforce Server, run
p4 configure set db.peeking=2
Any change to db.peeking
requires a server
restart to take effect.
The four values for db.peeking
are as follows:
|
Meaning |
---|---|
|
If This is the default behavior, and it corresponds to the behavior of Perforce at release 2013.2 and below. |
|
If This configuration is intended primarily for diagnostic purposes. |
|
If This configuration is expected to provide the best performance results for most sites. |
|
If
This configuration involves a trade-off between
concurrency and command completion speed; in general, if
a repository has many revisions per file, then some
commands will complete more slowly with
|
Commands implementing lockless reads
When peeking is enabled, the following commands run lockless:
Command |
Notes |
---|---|
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Applies to |
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when |
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Applies to |
|
when |
|
Applies to |
|
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|
The following commands run partially lockless; in most cases these commands will operate lock-free, but lockless operation is not guaranteed:
Command |
Notes |
---|---|
|
|
|
|
|
|
|
in the context of |
|
in the context of |
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|
Overriding the default behavior
After you have enabled peeking (by setting
db.peeking
to 1, 2, or 3 and restarting the
service), you can override the db.peeking
setting on a per-command basis by using the
-Zpeeking=
flag followed by your preferred
value. For example, to disable peeking for one command, run:
p4 -Zpeeking=1 fstat
and compare the results with:
p4 -Zpeeking=2 fstat
Measuring the effectiveness of lockless reads
In order to determine whether or not read locks are impacting
performance (and the extent to which enabling lockless reads has
improved performance), you can examine the server logs, or you can
use the -Ztrack
flag to output, for any given
command, the lines that would be written to the
P4LOG
. For example:
p4 -Zpeeking=1 -Ztrack sync
produces output for 11 database tables. The relevant lines here are
those that refer to "locks read/write
".
... --- db.counters --- pages in+out+cached 3+0+2 --- locks read/write 1/0 rows get+pos+scan put+del 1+0+0 0+0 --- db.user --- pages in+out+cached 3+0+2 --- locks read/write 1/0 rows get+pos+scan put+del 1+0+0 0+0 ...
The "1" appearing in ("locks read/write 1/0
")
every table's locking results shows one read lock taken per table.
By contrast, the diagnostic output from:
p4 -Zpeeking=2 -Ztrack sync
... --- db.counters --- pages in+out+cached 3+0+2 --- locks read/write 0/0 rows get+pos+scan put+del 1+0+0 0+0 ...
shows that the sync operation completed without any read or write
locks required on db.counters
(if you try it
yourself, on many other tables); when peeking is enabled, many
commands will show read/write 0/0
locks (or at
least, fewer locks) taken.
Side-track servers must have the same db.peeking level
A single Perforce instance can detect and ignore inadvertent
attempts to override db.peeking
that would
change table locking order and risk deadlock. (For example, if you
attempt to use db.peeking=3
on a server for
which peeking is disabled by having db.peeking
set to 0 (or unset), the service ignores the attempt altogether and
the command proceeds with the old behavior.
In the case of "side-track servers" described in the following Knowledge Base article:
http://answers.perforce.com/articles/KB_Article/Setting-Up-a-Side-track-Server
this protection is not available.
Warning!
All side-track servers must have the same
db.peeking
setting as the main server. Server
deadlock may result.
Diagnosing slow response times
Perforce is normally a light user of network resources. Although it is possible that an extremely large user operation could cause the Perforce server to respond slowly, consistently slow responses to p4 commands are usually caused by network problems. Any of the following can cause slow response times:
-
Misconfigured domain name system (DNS)
-
Misconfigured Windows networking
-
Difficulty accessing the p4 executable on a networked file system
A good initial test is to run p4 info. If this does not respond immediately, then there is a network problem. Although solving network problems is beyond the scope of this manual, here are some suggestions for troubleshooting them.
Hostname vs. IP address
Try setting P4PORT
to the service's IP address
instead of its hostname. For example, instead of using
P4PORT=host.domain:1666
try using
P4PORT=1.2.3.4:1666
with your site-specific IP address and port number.
On most systems, you can determine the IP address of a host by invoking:
ping hostname
If p4 info responds immediately when you use the IP address, but not when you use the hostname, the problem is likely related to DNS.
Windows wildcards
In some cases, p4 commands on Windows can result in a delayed response if they use unquoted filepatterns with a combination of depot syntax and wildcards, such as:
p4 files //depot/*
You can prevent the delay by putting double quotes around the file pattern, like this:
p4 files "//depot/*"
The cause of the problem is the p4 command's use
of a Windows function to expand wildcards. When quotes are not
used, the function interprets //depot
as a
networked computer path and spends time in a futile search for a
machine named depot
.
DNS lookups and the hosts file
On Windows, the
%SystemRoot%\system32\drivers\etc\hosts
file
can be used to hardcode IP address-hostname pairs. You might be
able to work around DNS problems by adding entries to this file.
The corresponding UNIX file is /etc/hosts
.
Location of the p4 executable
If none of the above diagnostic steps explains the sluggish response time, it's possible that the p4 executable itself is on a networked file system that is performing very poorly. To check this, try running:
p4 -V
This merely prints out the version information, without attempting any network access. If you get a slow response, network access to the p4 executable itself might be the problem. Copying or downloading a copy of p4 onto a local filesystem should improve response times.
Working over unreliable networks
To set a hard upper bound on how long a connection is willing to
wait on any single network read or write, set the
net.maxwait
configurable to the number of
seconds to wait before disconnecting with a network error. Users
working over unreliable connections can set
net.maxwait
value either in their
P4CONFIG
files, or use
-vnet.maxwait=
on a per-command basis, where t
t
is the
number of seconds to wait before timing out.
Note
Although net.maxwait
can be set on the
Perforce server, it is generally inadvisable to do so.For
example, if net.maxwait
is set to 60 on the
server, users of the Command-Line Client must complete every
interactive form within one minute before the command times out.
If, however, individual users set net.maxwait
in their own P4CONFIG
files (which reside on their
own workstations) their connections are not subject to this
limitation; commands only fail if the versioning service takes
more than 60 seconds to respond to their requests.
It is useful to combine net.maxwait
with the
-rN
global option, where
N
is the number of times to attempt
reconnection in the event that the network times out. For example:
p4 -r3 -vnet.maxwait=60 sync
attempts to sync the user's workspace, making up to three attempts to resume the sync if interrupted. The command fails after the third 60-second timeout.
Because the format of the output of a command that times out and is
restarted cannot be guaranteed (for example, if network
connectivity is broken in the middle of a line of output), avoid
the use of -r
on any command that reads from
standard input. For example, the behavior of the following command,
which reads a list of files from stdin and passes it to p4
add, can result in the attempted addition of "half a
filename" to the depot.
find . -print | p4 -x - -r3 add
To prevent this from happening (for example, if adding a large number of files over a very unreliable connection), consider an approach like the following:
find directoryname
-type f -exec p4 -r5 -vmax.netwait=60 add {} \;
All files (-type f
) in
directoryname
are found, and added one
at a time, by invoking the command "p4 -r5
-vmax.netwait=60 add" for each file individually.
After all files have been added, assign the changelist a changelist number with p4 change, and submit the numbered atomically with:
p4 -r5 -vmax.netwait=60 submit -c
changenum
If connectivity is interrupted, the numbered changelist submission is resumed.
Preventing server swamp
Generally, Perforce's performance depends on the number of files a user tries to manipulate in a single command invocation, not on the size of the depot. That is, syncing a client view of 30 files from a 3,000,000-file depot should not be much slower than syncing a client view of 30 files from a 30-file depot.
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.
When the server answers a request, it locks down the database for the duration of the computation phase. For normal operations, this is a successful strategy, because the server can "get in and out" quickly enough to avoid a backlog of requests. Abnormally large requests, however, can take seconds, sometimes even minutes. If frustrated users press CTRL-C and retry, the problem gets even worse; the server consumes more memory and responds even more slowly.
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
-
Limiting simultaneous connections with
server.maxcommands
-
Unloading infrequently-used metadata
-
Writing efficient scripts
-
Using compression efficiently
-
Other server configurables
Using tight views
The following "loose" view is trivial to set up but could invite trouble on a very large depot:
//depot/... //workspace/...
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:
//depot/main/srv/devA/... //workspace/main/srv/devA/... //depot/main/drv/lport/... //workspace/main/dvr/lport/... //depot/rel2.0/srv/devA/bin/... //workspace/rel2.0/srv/devA/bin/... //depot/qa/s6test/dvr/... //workspace/qa/s6test/dvr/...
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” and “The temporary client workspace trick”) 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
Protections (see Administering Perforce: Protections) are actually another type of Perforce view. Protections are set with the p4 protect command and control which depot files can be affected by commands run by users.
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:
write user sam * //depot/admin/... write group rocketdev * //depot/rocket/main/... write group rocketrel2 * //depot/rocket/rel2.0/...
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
Each Perforce group has an associated
maxresults, maxscanrows,
and maxlocktime value. The default for each is
unset
, but a superuser can use p4
group to limit it for any given group.
MaxResults prevents the server from using excessive memory by
limiting the amount of data buffered during command execution.
Users in limited groups are unable to run any commands that buffer
more database rows than the group's MaxResults
limit. (For most sites, MaxResults
should be
larger than the largest number of files anticipated in any one
user's individual client workspace.)
Like MaxResults
, MaxScanRows
prevents certain user commands from placing excessive demands on
the server. (Typically, the number of rows scanned in a single
operation is roughly equal to MaxResults
multiplied by the average number of revisions per file in the
depot.)
Finally, MaxLockTime
is used to prevent certain
commands from locking the database for prolonged periods of time.
Set MaxLockTime
to the number of milliseconds
for the longest permissible database lock.
To set these limits, fill in the appropriate fields in the
p4 group form. If a user is listed in multiple
groups, the highest of the
MaxResults
(or MaxScanRows
,
or MaxLockTime
) limits (including
unlimited
, but not
including the default unset
setting) for those
groups is taken as the user's MaxResults
(or
MaxScanRows
, or MaxLockTime
)
value.
Example 28. Effect of setting maxresults, maxscanrows, and maxlocktime.
As an administrator, you want members of the group
rocketdev
to be limited to operations of
20,000 files or less, that scan no more than 100,000 revisions,
and lock database tables for no more than 30 seconds:
Group: rocketdev MaxResults: 20000 MaxScanRows: 100000 MaxLockTime: 30000 Timeout: 43200 Subgroups: Owners: 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.
Regardless of which limits are in effect, no command she runs
will be permitted to lock the database for more than the
MaxLockTime
of 30000 milliseconds.
To remove any limits on the number of result lines processed (or
database rows scanned, or milliseconds of database locking time)
for a particular group, set the MaxResults
or
MaxScanRows
, or MaxLockTime
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. Because some Perforce applications can perform
large operations, you should typically set
MaxResults
no smaller than 10,000, set
MaxScanRows
no smaller than 50,000, and
MaxLockTime
to somewhere within the1000-30000
(1-30 second) range.
For more information, including a comparison of Perforce commands and the number of files they affect, type:
p4 help maxresults
p4 help maxscanrows
p4 help maxlocktime
from the command line.
MaxResults, MaxScanRows and MaxLockTime for users in multiple groups
As mentioned earlier, if a user is listed in multiple groups, the
highest numeric MaxResults
limit of all the
groups a user belongs to is the limit that affects the user.
The default value of unset
is
not a numeric limit; if a user is in a group
where MaxResults
is set to
unset
, he or she is still limited by the
highest numeric MaxResults
(or
MaxScanRows
or MaxLockTime
)
setting of the other groups of which he or she is a member.
A user's commands are truly unlimited only when the user belongs
to no groups, or when any of the groups of which the user is a
member have their MaxResults
set to
unlimited
.
Limiting simultaneous connections
If monitoring is enabled (p4 configure set
monitor=1 or higher), you can set the
server.maxcommands
configurable to limit the
number of simultaneous command requests that the service will
attempt to handle.
Ideally, this value should be set low enough to detect a runaway script or denial of service attack before the underlying hardware resources are exhausted, yet high enough to maintain a substantial margin of safety between the typical average number of connections and your site's peak activity.
If P4LOG
is set, the server log will contain lines
of the form:
Server is now using
nnn
active threads.
You can use the server log to determine what levels of activity are
typical for your site. As a general guideline, set
server.maxcommands
to at
least 200-500% of your anticipated peak activity.
Unloading infrequently-used metadata
Over time, a Perforce server accumulates metadata associated with
old projects that are no longer in active development. On large
sites, reducing the working set of data, (particularly that stored
in the db.have
and
db.labels
tables) can significantly improve
performance.
Create the unload depot
To create an unload depot named //unload
,
enter p4 depot unload, and fill in the
resulting form as follows:
Depot: unload Type: unload Map: unloaded/...
In this example, unloaded metadata is stored in flat files in the
/unloaded
directory beneath your server root
(that is, as specified by the Map:
field).
After you have created the unload depot, you can use p4 unload and p4 reload to manage your installation's handling of workspace and label-related metadata.
Unload old client workspaces, labels, and task streams
The p4 unload command transfers
infrequently-used metadata from the versioning engine's
db.*
files to a set of flat files in the
unload depot.
Individual users can use the -c
,
-l
, and -s
flags to
unload client workspaces, labels, or task streams that they own.
For example, maintainers of build scripts that create one
workspace and/or label per build, particularly in continuous
build environments, should be encouraged to unload the labels
after each build:
p4 unload -c oldworkspace
p4 unload -l oldlabel
Similarly, developers should be encouraged to unload (p4
unload -s oldtaskstream
) or
delete (p4 stream -d
oldtaskstream
) task streams
after use.
To manage old or obsolete metadata in bulk, administrators can
use the -a
, -al
, or
-ac
flags in conjunction with the
-d
and/or
date
-u
flags
to unload all labels and workspaces older than a specific
user
date
, owned by a specific
user
, or both.
By default, only unlocked labels or workspaces are unloaded; use
the -L
flag to unload locked labels or
workspaces.
To unload or reload a workspace or label, a user must be able to
scan all the files in the workspace's have
list and/or files tagged by the label. Set
MaxScanrows
and MaxResults
high enough (see “MaxResults, MaxScanRows and MaxLockTime for users in multiple groups”) that users do
not need to ask for assistance with p4 unload
or p4 reload operations.
Accessing unloaded data
By default, Perforce commands such as p4
clients, p4 labels, p4
files, p4 sizes, and p4
fstat ignore unloaded metadata. Users who need to
examine unloaded workspaces and labels (or other unloaded
metadata) can use the -U
flag when using
these commands. For more information, see the Command
Reference.
Reloading workspaces and labels
If it becomes necessary to restore unloaded metadata back into
the db.have
or
db.labels
table, use the p4
reload command.
Scripting efficiently
The Perforce Command-Line Client, p4, supports the scripting of any command that can be run interactively. The Perforce server can process commands far faster than users can issue them, so in an all-interactive environment, response time is excellent. However, p4 commands issued by scripts - triggers, review daemons, or command wrappers, for example - can cause performance problems if you haven't paid attention to their efficiency. This is not because p4 commands are inherently inefficient, but because the way one invokes p4 as an interactive user isn't necessarily suitable for repeated iterations.
This section points out some common efficiency problems and solutions.
Iterating through files
Each Perforce command issued causes a connection thread to be created and a p4d subprocess to be started. Reducing the number of Perforce commands your script runs is the first step to making it more efficient.
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
Instead of an inefficient approach like:
for i in `p4 files path1/...` do p4 diff2 path1/$i path2/$i [process diff output] done
Using list input files
Any Perforce command that accepts a list of files as a command-line argument can also read the same argument list from a file. Scripts can make use of the list input file feature by building up a list of files first, and then passing the list file to p4 -x.
For example, if your script might look something like this:
for components in header1 header2 header3 do p4 edit ${component}.h done
A more efficient alternative would be:
for components in header1 header2 header3 do echo ${component}.h >> LISTFILE done p4 -x LISTFILE edit
The -x
flag instructs p4 to read arguments, one per
line, from the named file. If the file is specified as
file
-
(a dash), the standard input is read.
By default, the server processes arguments from -x
in batches of 128
arguments at a a time; you can change the number of arguments
processed by the server by using the file
-b
flag to pass
arguments in different batch sizes.
batchsize
Using branch views
Branch views can be used with p4 integrate or p4 diff2 to reduce the number of Perforce command invocations. For example, you might have a script that runs:
p4 diff2 pathA/src/... pathB/src/...
p4 diff2 pathA/tests/... pathB/tests/...
p4 diff2 pathA/doc/... pathB/doc/...
You can make it more efficient by creating a branch view that looks like this:
Branch: pathA-pathB View: pathA/src/... pathB/src/... pathA/tests/... pathB/tests/... pathA/doc/... pathB/doc/...
...and replacing the three commands with one:
p4 diff2 -b pathA-pathB
Limiting label references
Repeated references to large labels can be particularly costly. Commands that refer to files using labels as revisions will scan the whole label once for each file argument. To keep from hogging the Perforce server, your script should get the labeled files from the server, and then scan the output for the files it needs.
For example, this:
p4 files path/...@label | egrep "path/f1.h|path/f2.h|path/f3.h"
imposes a lighter load on the Perforce server than either this:
p4 files path/f1.h@label path/f1.h@label path/f3.h@label
or this:
p4 files path/f1.h@label
p4 files path/f2.h@label
p4 files path/f3.h@label
The "temporary client workspace" trick described below can also reduce the number of times you have to refer to files by label.
On large sites, consider unloading infrequently-referenced or obsolete labels from the database. See “Unloading infrequently-used metadata”.
The temporary client workspace trick
Most Perforce commands can process all the files in the current workspace view with a single command-line argument. By making use of a temporary client workspace with a view that contains only the files on which you want to work, you might be able to reduce the number of commands you have to run, or to reduce the number of file arguments you need to give each command.
For instance, suppose your script runs these commands:
p4 sync pathA/src/...@label
p4 sync pathB/tests/...@label
p4 sync pathC/doc/...@label
You can combine the command invocations and reduce the three label scans to one by using a client workspace specification that looks like this:
Client: XY-temp View: pathA/src/... //XY-temp/pathA/src/... pathB/tests/... //XY-temp/pathB/tests/... pathC/doc/... //XY-temp/pathC/doc/...
Using this workspace specification, you can then run:
p4 -c XY-temp sync @label
Using compression efficiently
By default, revisions of files of type binary
are compressed when stored on the Perforce server. Some file
formats (for example, .GIF and .JPG images, .MPG and .AVI media
content, files compressed with .gz
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”.
Other server configurables
The Perforce server has many configurables that may be changed for performance purposes.
A complete list of configurables may be found by running p4 help configurables.
Parallel processing
When syncing your workspace, depending on the number and size of files being transferred,
the p4 synccommand might take a long time to execute. You can speed up
processing by having this command transfer files using multiple threads. You do this by
setting the net.parallel.max
configuration variable to a value greater than
one and by using the --parallel
option to the p4
sync command. Parallel processing is most effective with long-haul, high latency
networks or with other network configuration that prevents the use of available bandwidth with
a single TCP flow. Parallel processing might also be appropriate when working with large
compressed binary files, where the client must perform substantial work to decompress the
file.
See the description of the p4 sync command in the Perforce Command Reference for additional information.
Checkpoints for database tree rebalancing
Perforce's internal database stores its data in structures called Bayer trees, more commonly referred to as B-trees. While B-trees are a very common way to structure data for rapid access, over time, the process of adding and deleting elements to and from the trees can eventually lead to imbalances in the data structure.
Eventually, the tree can become sufficiently unbalanced that
performance is negatively affected. The Perforce checkpoint and
restore processes (see “Backup and recovery concepts”) 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.
The 2013.3 release of Perforce involves a change to the B-trees
that extends the limit on db.*
file size to 16TB
in length, as well as other significant scalability improvements.
The changes to the B-trees between Perforce 2013.2 and 2013.3 require that any upgrade that crosses this release boundary must be performed by taking a checkpoint with the older release and restoring that checkpoint with the newer release. See “Upgrading p4d - between 2013.2 and 2013.3” for details.