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Diffstat (limited to 'src/ceph/doc/dev/versions.rst')
| -rw-r--r-- | src/ceph/doc/dev/versions.rst | 42 |
1 files changed, 0 insertions, 42 deletions
diff --git a/src/ceph/doc/dev/versions.rst b/src/ceph/doc/dev/versions.rst deleted file mode 100644 index 34ed747..0000000 --- a/src/ceph/doc/dev/versions.rst +++ /dev/null @@ -1,42 +0,0 @@ -================== -Public OSD Version -================== - -We maintain two versions on disk: an eversion_t pg_log.head and a -version_t info.user_version. Each object is tagged with both the pg -version and user_version it was last modified with. The PG version is -modified by manipulating OpContext::at_version and then persisting it -to the pg log as transactions, and is incremented in all the places it -used to be. The user_version is modified by manipulating the new -OpContext::user_at_version and is also persisted via the pg log -transactions. -user_at_version is modified only in PrimaryLogPG::prepare_transaction -when the op was a "user modify" (a non-watch write), and the durable -user_version is updated according to the following rules: -1) set user_at_version to the maximum of ctx->new_obs.oi.user_version+1 -and info.last_user_version+1. -2) set user_at_version to the maximum of itself and -ctx->at_version.version. -3) ctx->new_obs.oi.user_version = ctx->user_at_version (to change the -object's user_version) - -This set of update semantics mean that for traditional pools the -user_version will be equal to the past reassert_version, while for -caching pools the object and PG user-version will be able to cross -pools without making a total mess of things. -In order to support old clients, we keep the old reassert_version but -rename it to "bad_replay_version"; we fill it in as before: for writes -it is set to the at_version (and is the proper replay version); for -watches it is set to our user version; for ENOENT replies it is set to -the replay version's epoch but the user_version's version. We also now -fill in the version_t portion of the bad_replay_version on read ops as -well as write ops, which should be fine for all old clients. - -For new clients, we prevent them from reading bad_replay_version and -add two proper members: user_version and replay_version; user_version -is filled in on every operation (reads included) while replay_version -is filled in for writes. - -The objclass function get_current_version() now always returns the -pg->info.last_user_version, which means it is guaranteed to contain -the version of the last user update in the PG (including on reads!). |