Partition - split up a standalone repo into a nested collection
Partition makes a directory of csetpruned components, moves them into place, then stitches them together into a product.
If partition were perfect, it could produce the same tree that would be produced by working in a nested collection all along. It would work as well as a standalone repo that could be rolled back to any point and give the same file layout.
Version 1.0 is not perfect, but pragmatic. This document has 2 parts: corners that were cut and overview of process.
Version 1.0 Corners that were cut
Cross component file moves — not handled at all. All user sfiles will look as though each spent its whole life in one component. The time where it was not in that component will be look like "BitKeeper/moved/<same-name-deleted-uses>" in that component.
Which component does a user sfile live in? There is the notion of a partition point — the first partition. In that partition, the deleted files are removed. That’s a reliable hack to get rid of trying to figure out what component(s) a deleted file lives in. The rest of the files are easy to categorize: BitKeeper/triggers - product BitKeeper - all components A/foo - A (if A is listed in the components file)
Incremental partitions use the name space defined by the partition point. Sfiles that are now deleted will be deleted in the same component(s) as the partition point. An sfile never changes components.
It is an error if a file moves across components between the first partition and an incremental partition. To address the error, the sfile can be moved back or deleted. The user really wants a cross component move in the incremental, he or she can do a bk cp and a bk rm of the original. Not ideal, but at least the user can keep working.
Larry mentioned providing a trigger could be pushed out into the standalones to recognize cross component file moves. That work has not been done.
Where the bookkeeping is weird: say we have two components, A and B, and foo moves from A to B. Partition is run, so it will look like foo always lived in B. A bk changes run in B will show foo’s changeset comments, and bk changes run in A will have nothing.
Options for the future? We might be able to clean up the bookkeeping in the future by using the :SORTKEY: to recover where the files in moved really lived. So we have at least left some bread crumbs to put things elsewhere.
Overview of Partition
The first partition and incremental partition are roughly the same. The main difference is for step one, the first partition defines what is in the gone and deleted list, and incremental partitions use that as a basis.
Make a work area
The cleanup prune of the standalone - remove gone and BitKeeper/deleted
Make components: clone and csetprune out non-component sfiles
Move components into place and gather up all their cset keys
Prune product and inject component csetkeys into product weave.
Attach (only on the first partition)
Partition clones a source repo to the location that will become the nested collection. In that cloned repo, a work area is setup in:
Most of the time in partition.c, the current directory is that work area. The macros WA and WA2PROD are used like ROOT2RESYNC and RESYNC2ROOT.
In the first partition, partition.c computes the gone list. See partition.c:cleanGone() for that. Incremental partitions use that same list.
csetprune.c:filterWeave() handles the removal of BitKeeper/deleted at the time of the partition point. Not a straightforward read, but it’s in there.
Also all BitKeeper/etc/gone files are replaced with one empty one that looks like it has been there for all time.
Components can be made in parallel by cloning the cleaned repo, then removing everything that is not in that component, and remapping the name of everything left.
For all names that are not in the component, csetprune.c:key2delName() is used to compute BitKeeper/moved/<same-as-deleted>
Each component at this stage is a functioning standalone repo: no BitKeeper/log/COMPONENTS or other meta data. It does not look like a detached; more like a pre-attached repo.
|csetprune left serials alone (using -N), so all the serials across all the repos line up.|
All the components get moved into place and their internals fixed up to look like a component with BitKeeper/log/COMPONENTS, and internal changeset file path names fixed.
Also all changeset keys are gathered up with: serial <tab> rootkey <space> deltakey
After those are gathered, the component changeset files are bk _scompress’d, so serials no longer line up.
A csetprune is done to get the same name mapping done for files in the product that had cross component history. Otherwise, the names will be the same.
Unique to this csetprune is the -W"PRODWEAVE" option, which injects into the weave, the keys gathered up in the previous stage. The effect is to replace all the file keys with corresponding component keys. This works because serials are kept constant in the component creation, so each component key will find the right product cset to live in.
Coverity suggested storing all components in the COMPS file passed to partition — both those being created by the prune and also attaches to be done. That way, everything is in one file.
This is done by filtering out all comps listed as <path>|<url> and running those as attaches after the product prune as been done.
New Gone’d files
New gone’d file — if after the first partition, files in the original standalone repo are gone’d, then an incremental partition is done, a new cset will be created which is an update to the gone files in the corresponding component. This works now.
The problem with making that new cset is every incremental partition done after this will also created a new cset with the same gone content.
Cross component file moves
After the first partition, if a user does a cross component file move in the standalone repo, an incremental partition will fail. The user will have the choice of moving the file back or to bk rm the file.
If a cross component move is needed, the user can introduce a new file by moving the file to a different name, and doing a bk cp to the new name, and doing a bk rm on the old name. That will work in an incremental partition and support in the user’s mind that it is a different file.
A trigger could be added to the standalone to detect the cross component move and either automate the shuffling or instruct the user on how to fix.
That trigger has not been written at this time.
Collisions between file and components
Long ago, a repo made have had a file called doc. At some point, that file was renamed, and a directory created called doc. Today, we want doc to be a component. Running a partition fails because a file delta doc overlaps with the component doc.
That will be fixed to in some cases, just work, and in some cases, map the name to the BitKeeper/moved directory. More will be detailed when that work is done.
5.0 could ship without it, since it will trigger a failure if it hits this condition and work without it. And we haven’t seen the condition tripped in the wild, and the beta’s have that wired to fail.
There will be unknown problems. As part of moving the partition code from shell to C, more staff understands the details. Hopefully, at worst, it may meaning take a partitioned repo a customer has and helping them pull data out of it into a new partition.
It can be made to go faster. Doing a clone and csetprune is inefficient. To do the unlink, each sfile is init’d to see that it is the correct file. There’s pretty simple changes to get it to skip the clone and init the file in the product repo. BK does that type of thing now in takepatch.c in applyCsetPatch to init the file in the main repo and write it in the RESYNC.
Not needed for 5.0, but certainly a good idea as far as future cleanups.
Other perf improvement is calculating csetfile checksum. That code has already had some pretty incredible perf work done. Try to read it without a piece of paper to draw out the data structures. Easy .. for Leonardo. Improvement can be done by making a more complex data structure to support incremental accumulation. Lotso work which only helps partition, and possibly huge pulls (through using cset_resum() in takepatch).
Probably better to put engineering time chaining to give a fast repo to users after the partition, instead of speeding up partition. However, if a compelling request comes in to make partition faster, know that it can be done.