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[Nvidia] Extracting Depot Paths Into New Instances of Their Own
MERGE 2013 THE PERFORCE CONFERENCE SAN FRANCISCO • APRIL 24−26Perforce White PaperTo provide a solid foundation for software developmentexcellence in today s demanding economy, it s criticalto have a software version management solution thatcan meet your demands.Extracting Depot Paths into NewInstances of Their OwnMark Warren, NVIDIA
2 Extracting Depot Paths into New Instances of Their Own INTRODUCTIONAs Perforce instances are used over time, they naturally grow in file and metadata size. Newfiles are submitted and metadata increases in size and the instance becomes unwieldy. Atsome point normal operations require table locks so long that all users are affected. To helpmitigate this problem, we can increase hardware performance but there is a limit to whathardware you can replace. A more practical method to release the building metadata pressureis to move select datasets to their own instance/depot.Perfsplit1I s a tool developed by Perforce that extracts a section of a depot from an existingPerforce database. It will access a Perforce server’s database directly and is platform andrelease specific. Perfsplit does not remove data from the source Perforce server but does copyarchive files from it. Perfsplit is a good tool for this operation but does not resolve some ofthese problems:• The need for zero downtime. Most instances that are in need of splitting have a verylarge user base. The need to keep instances up and running is compounded by thenumber of users unable to access their instance once this process in initiated.• Perfsplit does not rename the new instance depot. This is undesirable because it canbe confusing to users having the same depot name across multiple instances.• The need to use “p4 snap” to copy lazy integrated files to their physical lbr location. p4snap can considerably increase the size of the original depot depending on the size ofthe area we are splitting off.This white paper is intended to give guidelines on a method to resolve all these issues.Preparation To make sure we gather a complete dataset for migration from a live instance, it’s necessary toprevent users from making changes to the path(s) we are splitting. With super access rights,this can be done by simply restricting read-write access to this path and only allowing read-only. This restriction ensures that the metadata structure we are splitting off will be up to date.Once this is done, we need to create a checkpoint of the instance to gather lbr records and weneed to have a running instance of this checkpoint for Perfsplit use.Despite the inadequacies Perfsplit has, this process makes use of it; Perfsplit is necessary tobuild the foundation of the new instance. The key function of Perfsplit is using a map file todirect it to the select path(s) to extract. Because we are splitting not only the initial path(s) butalso the integration history, we will need to append this dataset to the splitmap. To get this, weneed to grep from the newly created original instances checkpoint the lbrFile record defined indb.rev2of all files associated with the depot path we are splitting. The lbrFile filename specifieswhere in the archives the file containing the revision may be found.For example: 1http://ftp.perforce.com/perforce/tools/perfsplit/perfsplit.html2http://www.perforce.com/perforce/doc.current/schema/#db.rev
3 Extracting Depot Paths into New Instances of Their Own grep @db.rev@ /checkpoint.XXX | grep //targeted/path/to/split/This will give you the db.rev entries for the path you want to split. From these entries you pullthe lbrFile column and remove all entries referring to the original path. This will give you thelocation of all lazy integrated files.Because we are not making use of the p4 snap feature, we will need to add these paths to thesplitmap (mapping) files already containing the path(s) we are splitting from the original depot.Transition Once we have this mapping, we can begin our split using Perfsplit with the minimum options,source, output, and splitmap file, but we also need an additional (undocumented) option “–a” toskip the Perfsplit archive file copy step. This will build a duplicate instance of the originalmetadata for all depots associated with the original split path in the output path. Because wedon’t want two instances with depots of the same name, we need to take another checkpoint ofthis new instance.Conversion With this new checkpoint, we can shape the metadata into a new data structure. To do this, webuild another instance from the newly created checkpoint, but during creation (replay) wemake some substitutions to point the current data structure to what we want.For example, to convert file paths from depot “foo” to depot “bar,” use the following commands:cat <checkpoint_file> | sed –e s#//foo/path/#//bar/path/# | p4d -r $p4root -f -jr –Now we have a new instance with the correct metadata.Connection The conversion now points the original metadata to a new depot area. We will need to createthis new depot “bar” to access this area. This new depot needs to be pointed to the split files.There are a number of options for the depot files. Depending on your situation, you can copythe files from the original location, leave them in the original location and symlink the newdepot to it, or move them to a new location and then symlink from the original depot location. Inevery situation, it is important to make sure the original depot does not have write access tothese files.Once this is done, you will have a new instance with a different name containing a completedata structure of split files.Verification Verification of the new instance should be run to test the success of the transfer. Only twoerrors can occur from a verify:
4 Extracting Depot Paths into New Instances of Their Own • Verification returns a "BAD" error. This is reported when the MD5 digest of a filerevision stored in the Perforce database differs from the one calculated by the “p4verify” command. This error indicates that the file revision might be corrupted. This ismost likely due to changes to the physical files during transfer. Otherwise, files shouldbe confirmed by someone familiar with them or by diffing them from the original.3• Verification returns a “MISSING” error. This indicates that Perforce cannot find thespecified revisions within the versioned file tree. Most likely this means the archive fileis missing from the versioned file tree. Check the lbrFile record of this file and makesure that this file is in its correct location, that the new instance can access thislocation, and that this file’s location was part of the splitmap.4Cleanup If you added paths to the splitmap to capture the lazy integrated files, these depots/files will beaccessible in the new instance. These are necessary for the new instance to locate these filesbut can make the new instance look cluttered because they are not part of the originalintended split path. Because these paths are only for the instance to locate and not for userinteraction, these extra depots/files can be removed/hidden from user view by restricting theirview in the protection table. This will make the new instance look like it only has the intendedsplit depot path and still allow the instance access.Completion By implementing these steps using Perfsplit, the issues regarding zero downtime, duplicatenaming, and integration history are addressed. Resolution of these issues makes Perfsplit amore desirable tool in a large installation environment. 3http://answers.perforce.com/articles/KB_Article/How-to-Handle-p4-verify-BAD-Errors4http://answers.perforce.com/articles/KB_Article/MISSING-errors-from-p4-verify