The key change in v2 is the inbox is no longer a bare git
repository, but a directory with two or more git repositories.
v2 divides git repositories by time "epochs" and Xapian
-databases for parallelism by "partitions".
+databases for parallelism by "shards".
=head2 INBOX OVERVIEW AND DEFINITIONS
- inbox.lock # lock file (flock) to protect global state
- git/$EPOCH.git # normal git repositories
- all.git # empty git repo, alternates to git/$EPOCH.git
-- xap$SCHEMA_VERSION/$PART # per-partition Xapian DB
+- xap$SCHEMA_VERSION/$SHARD # per-shard Xapian DB
- xap$SCHEMA_VERSION/over.sqlite3 # OVER-view DB for NNTP and threading
- msgmap.sqlite3 # same the v1 msgmap
L<https://public-inbox.org/meta/20180209205140.GA11047@dcvr/>
-=head2 XAPIAN PARTITIONS
+=head2 XAPIAN SHARDS
Another second scalability problem in v1 was the inability to
utilize multiple CPU cores for Xapian indexing. This is
-addressed by using partitions in Xapian to perform import
+addressed by using shards in Xapian to perform import
indexing in parallel.
As with git alternates, Xapian natively supports a read-only
interface which transparently abstracts away the knowledge of
-multiple partitions. This allows us to simplify our read-only
+multiple shards. This allows us to simplify our read-only
code paths.
The performance of the storage device is now the bottleneck on
small instances.
Our use of the L</OVERVIEW DB> requires Xapian document IDs to
-remain stable. Thus, use of L<xapian-compact(1)> and
-L<copydatabase(8)> require the use of C<--no-renumber> switch.
+remain stable. Using L<public-inbox-compact(1)> and
+L<public-inbox-xcpdb(1)> wrappers are recommended over tools
+provided by Xapian.
=head2 OVERVIEW DB
to implement the NNTP OVER/XOVER commands and non-search
endpoints of of the PSGI UI.
-In the future, Xapian will become completely optional for v2 (as
-it is for v1) as SQLite turns out to be powerful enough to
-maintain overview information. Most of the PSGI and all of the
-NNTP functionality will be possible with only SQLite in addition
+Xapian has become completely optional for v2 (as it is for v1), but
+SQLite remains required for v2. SQLite turns out to be powerful
+enough to maintain overview information. Most of the PSGI and all
+of the NNTP functionality is possible with only SQLite in addition
to git.
The overview DB was an instrumental piece in maintaining near