An upgrade of a repository created with recommended settings only suggests optimizations

  $ hg init empty

  $ cd empty

  $ hg debugupgraderepo

  (no feature deficiencies found in existing repository)

  performing an upgrade with "--run" will make the following changes:

  requirements

     preserved: dotencode, fncache, generaldelta, revlogv1, store

  additional optimizations are available by specifying "--optimize <name>":

  redeltaparent

     deltas within internal storage will be recalculated to choose an optimal base revision where this was not already done; the size of the repository may shrink and various operations may become faster; the first time this optimization is performed could slow down upgrade execution considerably; subsequent invocations should not run noticeably slower

  redeltamultibase

     deltas within internal storage will be recalculated against multiple base revision and the smallest difference will be used; the size of the repository may shrink significantly when there are many merges; this optimization will slow down execution in proportion to the number of merges in the repository and the amount of files in the repository; this slow down should not be significant unless there are tens of thousands of files and thousands of merges

  redeltaall

     deltas within internal storage will always be recalculated without reusing prior deltas; this will likely make execution run several times slower; this optimization is typically not needed

--optimize can be used to add optimizations

  $ hg debugupgrade --optimize redeltaparent

  (no feature deficiencies found in existing repository)

  performing an upgrade with "--run" will make the following changes:

  requirements

     preserved: dotencode, fncache, generaldelta, revlogv1, store

  redeltaparent

     deltas within internal storage will choose a new base revision if needed

  additional optimizations are available by specifying "--optimize <name>":

  redeltamultibase

     deltas within internal storage will be recalculated against multiple base revision and the smallest difference will be used; the size of the repository may shrink significantly when there are many merges; this optimization will slow down execution in proportion to the number of merges in the repository and the amount of files in the repository; this slow down should not be significant unless there are tens of thousands of files and thousands of merges

  redeltaall

     deltas within internal storage will always be recalculated without reusing prior deltas; this will likely make execution run several times slower; this optimization is typically not needed

Various sub-optimal detections work

  $ cat > .hg/requires << EOF

  > revlogv1

  > store

  > EOF

  $ hg debugupgraderepo

  repository lacks features recommended by current config options:

  fncache

     long and reserved filenames may not work correctly; repository performance is sub-optimal

  dotencode

     storage of filenames beginning with a period or space may not work correctly

  generaldelta

     deltas within internal storage are unable to choose optimal revisions; repository is larger and slower than it could be; interaction with other repositories may require extra network and CPU resources, making "hg push" and "hg pull" slower

  performing an upgrade with "--run" will make the following changes:

  requirements

     preserved: revlogv1, store

     added: dotencode, fncache, generaldelta

  fncache

     repository will be more resilient to storing certain paths and performance of certain operations should be improved

  dotencode

     repository will be better able to store files beginning with a space or period

  generaldelta

     repository storage will be able to create optimal deltas; new repository data will be smaller and read times should decrease; interacting with other repositories using this storage model should require less network and CPU resources, making "hg push" and "hg pull" faster

  additional optimizations are available by specifying "--optimize <name>":

  redeltaparent

     deltas within internal storage will be recalculated to choose an optimal base revision where this was not already done; the size of the repository may shrink and various operations may become faster; the first time this optimization is performed could slow down upgrade execution considerably; subsequent invocations should not run noticeably slower

  redeltamultibase

     deltas within internal storage will be recalculated against multiple base revision and the smallest difference will be used; the size of the repository may shrink significantly when there are many merges; this optimization will slow down execution in proportion to the number of merges in the repository and the amount of files in the repository; this slow down should not be significant unless there are tens of thousands of files and thousands of merges

  redeltaall

     deltas within internal storage will always be recalculated without reusing prior deltas; this will likely make execution run several times slower; this optimization is typically not needed

  $ hg --config format.dotencode=false debugupgraderepo

  repository lacks features recommended by current config options:

  fncache

     long and reserved filenames may not work correctly; repository performance is sub-optimal

  generaldelta

     deltas within internal storage are unable to choose optimal revisions; repository is larger and slower than it could be; interaction with other repositories may require extra network and CPU resources, making "hg push" and "hg pull" slower

  repository lacks features used by the default config options:

  dotencode

     storage of filenames beginning with a period or space may not work correctly

  performing an upgrade with "--run" will make the following changes:

  requirements

     preserved: revlogv1, store

     added: fncache, generaldelta

  fncache

     repository will be more resilient to storing certain paths and performance of certain operations should be improved

  generaldelta

     repository storage will be able to create optimal deltas; new repository data will be smaller and read times should decrease; interacting with other repositories using this storage model should require less network and CPU resources, making "hg push" and "hg pull" faster

  additional optimizations are available by specifying "--optimize <name>":

  redeltaparent

     deltas within internal storage will be recalculated to choose an optimal base revision where this was not already done; the size of the repository may shrink and various operations may become faster; the first time this optimization is performed could slow down upgrade execution considerably; subsequent invocations should not run noticeably slower

  redeltamultibase

     deltas within internal storage will be recalculated against multiple base revision and the smallest difference will be used; the size of the repository may shrink significantly when there are many merges; this optimization will slow down execution in proportion to the number of merges in the repository and the amount of files in the repository; this slow down should not be significant unless there are tens of thousands of files and thousands of merges

  redeltaall

     deltas within internal storage will always be recalculated without reusing prior deltas; this will likely make execution run several times slower; this optimization is typically not needed