diff --git a/sql/swh-func.sql b/sql/swh-func.sql
index cb782344..70596e00 100644
--- a/sql/swh-func.sql
+++ b/sql/swh-func.sql
@@ -1,655 +1,658 @@
 
 -- create a temporary table called tmp_TBLNAME, mimicking existing table
 -- TBLNAME
 --
 -- Args:
 --     tblname: name of the table to mimick
 create or replace function swh_mktemp(tblname regclass)
     returns void
     language plpgsql
 as $$
 begin
     execute format('
 	create temporary table tmp_%I
 	    (like %I including defaults)
 	    on commit drop
 	', tblname, tblname);
     return;
 end
 $$;
 
 
 -- create a temporary table for directory entries called tmp_TBLNAME,
 -- mimicking existing table TBLNAME with an extra dir_id (sha1_git)
 -- column, and dropping the id column.
 --
 -- This is used to create the tmp_directory_entry_<foo> tables.
 --
 -- Args:
 --     tblname: name of the table to mimick
 create or replace function swh_mktemp_dir_entry(tblname regclass)
     returns void
     language plpgsql
 as $$
 begin
     execute format('
 	create temporary table tmp_%I
 	    (like %I including defaults, dir_id sha1_git)
 	    on commit drop;
         alter table tmp_%I drop column id;
 	', tblname, tblname, tblname, tblname);
     return;
 end
 $$;
 
 
 -- create a temporary table for revisions called tmp_revisions,
 -- mimicking existing table revision, replacing the foreign keys to
 -- people with an email and name field
 --
 create or replace function swh_mktemp_revision()
     returns void
     language sql
 as $$
     create temporary table tmp_revision (
         like revision including defaults,
         author_name text not null default '',
         author_email text not null default '',
         committer_name text not null default '',
         committer_email text not null default ''
     ) on commit drop;
     alter table tmp_revision drop column author;
     alter table tmp_revision drop column committer;
 $$;
 
 
 -- create a temporary table for releases called tmp_release,
 -- mimicking existing table release, replacing the foreign keys to
 -- people with an email and name field
 --
 create or replace function swh_mktemp_release()
     returns void
     language sql
 as $$
     create temporary table tmp_release (
         like release including defaults,
         author_name text not null default '',
         author_email text not null default ''
     ) on commit drop;
     alter table tmp_release drop column author;
 $$;
 
 
 -- a content signature is a set of cryptographic checksums that we use to
 -- uniquely identify content, for the purpose of verifying if we already have
 -- some content or not during content injection
 create type content_signature as (
     sha1      sha1,
     sha1_git  sha1_git,
     sha256    sha256
 );
 
 
 -- check which entries of tmp_content are missing from content
 --
 -- operates in bulk: 0. swh_mktemp(content), 1. COPY to tmp_content,
 -- 2. call this function
 create or replace function swh_content_missing()
     returns setof content_signature
     language plpgsql
 as $$
 begin
     -- This query is critical for (single-algorithm) hash collision detection,
     -- so we cannot rely only on the fact that a single hash (e.g., sha1) is
     -- missing from the table content to conclude that a given content is
     -- missing. Ideally, we would want to (try to) add to content all entries
     -- in tmp_content that, when considering all columns together, are missing
     -- from content.
     --
     -- But doing that naively would require a *compound* index on all checksum
     -- columns; that index would not be significantly smaller than the content
     -- table itself, and therefore won't be used. Therefore we union together
     -- all contents that differ on at least one column from what is already
     -- available. If there is a collision on some (but not all) columns, the
     -- relevant tmp_content entry will be included in the set of content to be
     -- added, causing a downstream violation of unicity constraint.
     return query
 	(select sha1, sha1_git, sha256 from tmp_content as tmp
 	 where not exists
 	     (select 1 from content as c where c.sha1 = tmp.sha1))
 	union
 	(select sha1, sha1_git, sha256 from tmp_content as tmp
 	 where not exists
 	     (select 1 from content as c where c.sha1_git = tmp.sha1_git))
 	union
 	(select sha1, sha1_git, sha256 from tmp_content as tmp
 	 where not exists
 	     (select 1 from content as c where c.sha256 = tmp.sha256));
     return;
 end
 $$;
 
 
 -- check which entries of tmp_skipped_content are missing from skipped_content
 --
 -- operates in bulk: 0. swh_mktemp(skipped_content), 1. COPY to tmp_skipped_content,
 -- 2. call this function
 create or replace function swh_skipped_content_missing()
     returns setof content_signature
     language plpgsql
 as $$
 begin
     return query
 	select sha1, sha1_git, sha256 from tmp_skipped_content
 	where not exists
 	(select 1 from skipped_content s where
 	    sha1 is not distinct from s.sha1 and
 	    sha1_git is not distinct from s.sha1_git and
 	    sha256 is not distinct from s.sha256);
     return;
 end
 $$;
 
 
 -- Look up content based on one or several different checksums. Return all
 -- content information if the content is found; a NULL row otherwise.
 --
 -- At least one checksum should be not NULL. If several are not NULL, they will
 -- be AND-ed together in the lookup query.
 --
 -- Note: this function is meant to be used to look up individual contents
 -- (e.g., for the web app), for batch lookup of missing content (e.g., to be
 -- added) see swh_content_missing
 create or replace function swh_content_find(
     sha1      sha1     default NULL,
     sha1_git  sha1_git default NULL,
     sha256    sha256   default NULL
 )
     returns content
     language plpgsql
 as $$
 declare
     con content;
     filters text[] := array[] :: text[];  -- AND-clauses used to filter content
     q text;
 begin
     if sha1 is not null then
         filters := filters || format('sha1 = %L', sha1);
     end if;
     if sha1_git is not null then
         filters := filters || format('sha1_git = %L', sha1_git);
     end if;
     if sha256 is not null then
         filters := filters || format('sha256 = %L', sha256);
     end if;
 
     if cardinality(filters) = 0 then
         return null;
     else
         q = format('select * from content where %s',
 	        array_to_string(filters, ' and '));
         execute q into con;
 	return con;
     end if;
 end
 $$;
 
 
 -- add tmp_content entries to content, skipping duplicates
 --
 -- operates in bulk: 0. swh_mktemp(content), 1. COPY to tmp_content,
 -- 2. call this function
 create or replace function swh_content_add()
     returns void
     language plpgsql
 as $$
 begin
     insert into content (sha1, sha1_git, sha256, length, status)
 	select distinct sha1, sha1_git, sha256, length, status
 	from tmp_content
 	where (sha1, sha1_git, sha256) in
 	    (select * from swh_content_missing());
 	    -- TODO XXX use postgres 9.5 "UPSERT" support here, when available.
 	    -- Specifically, using "INSERT .. ON CONFLICT IGNORE" we can avoid
 	    -- the extra swh_content_missing() query here.
     return;
 end
 $$;
 
 
 -- add tmp_skipped_content entries to skipped_content, skipping duplicates
 --
 -- operates in bulk: 0. swh_mktemp(skipped_content), 1. COPY to tmp_skipped_content,
 -- 2. call this function
 create or replace function swh_skipped_content_add()
     returns void
     language plpgsql
 as $$
 begin
     insert into skipped_content (sha1, sha1_git, sha256, length, status, reason, origin)
 	select distinct sha1, sha1_git, sha256, length, status, reason, origin
 	from tmp_skipped_content
 	where (coalesce(sha1, ''), coalesce(sha1_git, ''), coalesce(sha256, '')) in
 	    (select coalesce(sha1, ''), coalesce(sha1_git, ''), coalesce(sha256, '') from swh_skipped_content_missing());
 	    -- TODO XXX use postgres 9.5 "UPSERT" support here, when available.
 	    -- Specifically, using "INSERT .. ON CONFLICT IGNORE" we can avoid
 	    -- the extra swh_content_missing() query here.
     return;
 end
 $$;
 
 
 -- check which entries of tmp_directory are missing from directory
 --
 -- operates in bulk: 0. swh_mktemp(directory), 1. COPY to tmp_directory,
 -- 2. call this function
 create or replace function swh_directory_missing()
     returns setof sha1_git
     language plpgsql
 as $$
 begin
     return query
 	select id from tmp_directory
-	except
-	select id from directory;
+	where not exists (
+	    select 1 from directory d
+	    where d.id = id);
     return;
 end
 $$;
 
 
 create type directory_entry_type as enum('file', 'dir', 'rev');
 
 
 -- Add tmp_directory_entry_* entries to directory_entry_* and directory,
 -- skipping duplicates in directory_entry_*.  This is a generic function that
 -- works on all kind of directory entries.
 --
 -- operates in bulk: 0. swh_mktemp_dir_entry('directory_entry_*'), 1 COPY to
 -- tmp_directory_entry_*, 2. call this function
 --
 -- Assumption: this function is used in the same transaction that inserts the
 -- context directory in table "directory".
 create or replace function swh_directory_entry_add(typ directory_entry_type)
     returns void
     language plpgsql
 as $$
 begin
     execute format('
     insert into directory_entry_%1$s (target, name, perms)
     select distinct t.target, t.name, t.perms
     from tmp_directory_entry_%1$s t
     where not exists (
     select 1
     from directory_entry_%1$s i
     where t.target = i.target and t.name = i.name and t.perms = i.perms)
    ', typ);
 
     execute format('
     with new_entries as (
 	select t.dir_id, array_agg(i.id) as entries
 	from tmp_directory_entry_%1$s t
 	inner join directory_entry_%1$s i
 	using (target, name, perms)
 	group by t.dir_id
     )
     update directory as d
     set %1$s_entries = new_entries.entries
     from new_entries
     where d.id = new_entries.dir_id
     ', typ);
 
     return;
 end
 $$;
 
 
 -- a directory listing entry with all the metadata
 --
 -- can be used to list a directory, and retrieve all the data in one go.
 create type directory_entry as
 (
   dir_id  sha1_git,     -- id of the parent directory
   type    directory_entry_type,  -- type of entry
   target  sha1_git,     -- id of target
   name    unix_path,    -- path name, relative to containing dir
   perms   file_perms    -- unix-like permissions
 );
 
 
 -- List a single level of directory walked_dir_id
 create or replace function swh_directory_walk_one(walked_dir_id sha1_git)
     returns setof directory_entry
     language sql
 as $$
     with dir as (
 	select id as dir_id, dir_entries, file_entries, rev_entries
 	from directory
 	where id = walked_dir_id),
     ls_d as (select dir_id, unnest(dir_entries) as entry_id from dir),
     ls_f as (select dir_id, unnest(file_entries) as entry_id from dir),
     ls_r as (select dir_id, unnest(rev_entries) as entry_id from dir)
     (select dir_id, 'dir'::directory_entry_type as type,
 	    target, name, perms
      from ls_d
      left join directory_entry_dir d on ls_d.entry_id = d.id)
     union
     (select dir_id, 'file'::directory_entry_type as type,
 	    target, name, perms
      from ls_f
      left join directory_entry_file d on ls_f.entry_id = d.id)
     union
     (select dir_id, 'rev'::directory_entry_type as type,
 	    target, name, perms
      from ls_r
      left join directory_entry_rev d on ls_r.entry_id = d.id)
     order by name;
 $$;
 
 
 -- List all revision IDs starting from a given revision, going back in time
 --
 -- TODO ordering: should be breadth-first right now (what do we want?)
 -- TODO ordering: ORDER BY parent_rank somewhere?
 create or replace function swh_revision_list(root_revision sha1_git)
     returns setof sha1_git
     language sql
 as $$
     with recursive rev_list(id) as (
 	(select id from revision where id = root_revision)
 	union
 	(select parent_id
 	 from revision_history as h
 	 join rev_list on h.id = rev_list.id)
     )
     select * from rev_list;
 $$;
 
 
 -- Detailed entry in a revision log
 create type revision_log_entry as
 (
   id                     sha1_git,
   date                   timestamptz,
   date_offset            smallint,
   committer_date         timestamptz,
   committer_date_offset  smallint,
   type                   revision_type,
   directory              sha1_git,
   message                bytea,
   author_name            text,
   author_email           text,
   committer_name         text,
   committer_email        text
 );
 
 
 -- "git style" revision log. Similar to swh_revision_list(), but returning all
 -- information associated to each revision, and expanding authors/committers
 create or replace function swh_revision_log(root_revision sha1_git)
     returns setof revision_log_entry
     language sql
 as $$
     select revision.id, date, date_offset,
 	committer_date, committer_date_offset,
 	type, directory, message,
 	author.name as author_name, author.email as author_email,
 	committer.name as committer_name, committer.email as committer_email
     from swh_revision_list(root_revision) as rev_list
     join revision on revision.id = rev_list
     join person as author on revision.author = author.id
     join person as committer on revision.committer = committer.id;
 $$;
 
 
 -- List missing revisions from tmp_revision
 create or replace function swh_revision_missing()
     returns setof sha1_git
     language plpgsql
 as $$
 begin
     return query
         select id from tmp_revision
-	except
-	select id from revision;
+	where not exists (
+	    select 1 from revision r
+	    where r.id = id);
     return;
 end
 $$;
 
 
 -- Create entries in person from tmp_revision
 create or replace function swh_person_add_from_revision()
     returns void
     language plpgsql
 as $$
 begin
     with t as (
         select author_name as name, author_email as email from tmp_revision
     union
         select committer_name as name, committer_email as email from tmp_revision
     ) insert into person (name, email)
     select distinct name, email from t
     where not exists (
         select 1
 	from person p
 	where t.name = p.name and t.email = p.email
     );
     return;
 end
 $$;
 
 
 -- Create entries in revision from tmp_revision
 create or replace function swh_revision_add()
     returns void
     language plpgsql
 as $$
 begin
     perform swh_person_add_from_revision();
 
     insert into revision (id, date, date_offset, committer_date, committer_date_offset, type, directory, message, author, committer)
     select t.id, t.date, t.date_offset, t.committer_date, t.committer_date_offset, t.type, t.directory, t.message, a.id, c.id
     from tmp_revision t
     left join person a on a.name = t.author_name and a.email = t.author_email
     left join person c on c.name = t.committer_name and c.email = t.committer_email;
     return;
 end
 $$;
 
 
 -- List missing releases from tmp_release
 create or replace function swh_release_missing()
     returns setof sha1_git
     language plpgsql
 as $$
 begin
     return query
         select id from tmp_release
-	except
-	select id from release;
+	where not exists (
+	select 1 from release r
+	where r.id = id);
     return;
 end
 $$;
 
 
 -- Create entries in person from tmp_release
 create or replace function swh_person_add_from_release()
     returns void
     language plpgsql
 as $$
 begin
     with t as (
         select distinct author_name as name, author_email as email from tmp_release
     ) insert into person (name, email)
     select name, email from t
     where not exists (
         select 1
 	from person p
 	where t.name = p.name and t.email = p.email
     );
     return;
 end
 $$;
 
 
 -- Create entries in release from tmp_release
 create or replace function swh_release_add()
     returns void
     language plpgsql
 as $$
 begin
     perform swh_person_add_from_release();
 
     insert into release (id, revision, date, date_offset, name, comment, author)
     select t.id, t.revision, t.date, t.date_offset, t.name, t.comment, a.id
     from tmp_release t
     left join person a on a.name = t.author_name and a.email = t.author_email;
     return;
 end
 $$;
 
 
 -- Absolute path: directory reference + complete path relative to it
 create type content_dir as (
     directory  sha1_git,
     path       unix_path
 );
 
 
 -- Find the containing directory of a given content, specified by sha1
 -- (note: *not* sha1_git).
 --
 -- Return a pair (dir_it, path) where path is a UNIX path that, from the
 -- directory root, reach down to a file with the desired content. Return NULL
 -- if no match is found.
 --
 -- In case of multiple paths (i.e., pretty much always), an arbitrary one is
 -- chosen.
 create or replace function swh_content_find_directory(content_id sha1)
     returns content_dir
     language sql
 as $$
     with recursive path as (
 	-- Recursively build a path from the requested content to a root
 	-- directory. Each iteration returns a pair (dir_id, filename) where
 	-- filename is relative to dir_id. Stops when no parent directory can
 	-- be found.
 	(select dir.id as dir_id, dir_entry_f.name as name, 0 as depth
 	 from directory_entry_file as dir_entry_f
 	 join content on content.sha1_git = dir_entry_f.target
 	 join directory as dir on dir.file_entries @> array[dir_entry_f.id]
 	 where content.sha1 = content_id
 	 limit 1)
 	union all
 	(select dir.id as dir_id,
 		(dir_entry_d.name || '/' || path.name)::unix_path as name,
 		path.depth + 1
 	 from path
 	 join directory_entry_dir as dir_entry_d on dir_entry_d.target = path.dir_id
 	 join directory as dir on dir.dir_entries @> array[dir_entry_d.id]
 	 limit 1)
     )
     select dir_id, name from path order by depth desc limit 1;
 $$;
 
 
 -- Walk the revision history starting from a given revision, until a matching
 -- occurrence is found. Return all occurrence information if one is found, NULL
 -- otherwise.
 create or replace function swh_revision_find_occurrence(revision_id sha1_git)
     returns occurrence
     language plpgsql
 as $$
 declare
     occ occurrence%ROWTYPE;
     rev sha1_git;
 begin
     -- first check to see if revision_id is already pointed by an occurrence
     select origin, branch, revision
     from occurrence_history as occ_hist
     where occ_hist.revision = revision_id
     order by upper(occ_hist.validity)  -- TODO filter by authority?
     limit 1
     into occ;
 
     -- no occurrence point to revision_id, walk up the history
     if not found then
         -- recursively walk the history, stopping immediately before a revision
         -- pointed to by an occurrence.
 	-- TODO find a nicer way to stop at, but *including*, that revision
 	with recursive revlog as (
 	    (select revision_id as rev_id, 0 as depth)
 	    union all
 	    (select hist.parent_id as rev_id, revlog.depth + 1
 	     from revlog
 	     join revision_history as hist on hist.id = revlog.rev_id
 	     and not exists(select 1 from occurrence_history
 			    where revision = hist.parent_id)
 	     limit 1)
 	)
 	select rev_id from revlog order by depth desc limit 1
 	into rev;
 	if not found then return null; end if;
 
 	-- as we stopped before a pointed by revision, look it up again and
 	-- return its data
 	select origin, branch, revision
 	from revision_history as rev_hist, occurrence_history as occ_hist
 	where rev_hist.id = rev
 	and occ_hist.revision = rev_hist.parent_id
 	order by upper(occ_hist.validity)  -- TODO filter by authority?
 	limit 1
 	into occ;
     end if;
 
     return occ;  -- might be NULL
 end
 $$;
 
 
 -- Occurrence of some content in a given context
 create type content_occurrence as (
     origin_type	 text,
     origin_url	 text,
     branch	 text,
     revision_id	 sha1_git,
     path	 unix_path
 );
 
 
 -- Given the sha1 of some content, look up an occurrence that points to a
 -- revision, which in turns reference (transitively) a tree containing the
 -- content. Answer the question: "where/when did SWH see a given content"?
 -- Return information about an arbitrary occurrence/revision/tree if one is
 -- found, NULL otherwise.
 create or replace function swh_content_find_occurrence(content_id sha1)
     returns content_occurrence
     language plpgsql
 as $$
 declare
     dir content_dir;
     rev sha1_git;
     occ occurrence%ROWTYPE;
     coc content_occurrence;
 begin
     -- each step could fail if no results are found, and that's OK
     select * from swh_content_find_directory(content_id)     -- look up directory
 	into dir;
     if not found then return null; end if;
 
     select id from revision where directory = dir.directory  -- look up revision
 	limit 1
 	into rev;
     if not found then return null; end if;
 
     select * from swh_revision_find_occurrence(rev)	     -- look up occurrence
 	into occ;
     if not found then return null; end if;
 
     select origin.type, origin.url, occ.branch, rev, dir.path
     from origin
     where origin.id = occ.origin
     into coc;
 
     return coc;  -- might be NULL
 end
 $$;
diff --git a/sql/swh-schema.sql b/sql/swh-schema.sql
index 276cf9dc..ac53056a 100644
--- a/sql/swh-schema.sql
+++ b/sql/swh-schema.sql
@@ -1,324 +1,324 @@
 ---
 --- Software Heritage Data Model
 ---
 
 -- drop schema if exists swh cascade;
 -- create schema swh;
 -- set search_path to swh;
 
 create table dbversion
 (
   version     int primary key,
   release     timestamptz,
   description text
 );
 
 insert into dbversion(version, release, description)
-      values(18, now(), 'Work In Progress');
+      values(19, now(), 'Work In Progress');
 
 -- a SHA1 checksum (not necessarily originating from Git)
 create domain sha1 as bytea check (length(value) = 20);
 
 -- a Git object ID, i.e., a SHA1 checksum
 create domain sha1_git as bytea check (length(value) = 20);
 
 -- a SHA256 checksum
 create domain sha256 as bytea check (length(value) = 32);
 
 -- UNIX path (absolute, relative, individual path component, etc.)
 create domain unix_path as bytea;
 
 -- a set of UNIX-like access permissions, as manipulated by, e.g., chmod
 create domain file_perms as int;
 
 create type content_status as enum ('absent', 'visible', 'hidden');
 
 -- An origin is a place, identified by an URL, where software can be found. We
 -- support different kinds of origins, e.g., git and other VCS repositories,
 -- web pages that list tarballs URLs (e.g., http://www.kernel.org), indirect
 -- tarball URLs (e.g., http://www.example.org/latest.tar.gz), etc. The key
 -- feature of an origin is that it can be *fetched* (wget, git clone, svn
 -- checkout, etc.) to retrieve all the contained software.
 create table origin
 (
   id         bigserial primary key,
   type       text, -- TODO use an enum here (?)
   url        text not null
 );
 
 -- Checksums about actual file content. Note that the content itself is not
 -- stored in the DB, but on external (key-value) storage. A single checksum is
 -- used as key there, but the other can be used to verify that we do not inject
 -- content collisions not knowingly.
 create table content
 (
   sha1      sha1 primary key,
   sha1_git  sha1_git not null,
   sha256    sha256 not null,
   length    bigint not null,
   ctime     timestamptz not null default now(),
             -- creation time, i.e. time of (first) injection into the storage
   status    content_status not null default 'visible'
 );
 
 create unique index on content(sha1_git);
 create unique index on content(sha256);
 
 -- Content we have seen but skipped for some reason. This table is
 -- separate from the content table as we might not have the sha1
 -- checksum of that data (for instance when we inject git
 -- repositories, objects that are too big will be skipped here, and we
 -- will only know their sha1_git). 'reason' contains the reason the
 -- content was skipped. origin is a nullable column allowing to find
 -- out which origin contains that skipped content.
 create table skipped_content
 (
   sha1      sha1,
   sha1_git  sha1_git,
   sha256    sha256,
   length    bigint not null,
   ctime     timestamptz not null default now(),
   status    content_status not null default 'absent',
   reason    text not null,
   origin    bigint references origin(id),
   unique (sha1, sha1_git, sha256)
 );
 
 -- those indexes support multiple NULL values.
 create unique index on skipped_content(sha1);
 create unique index on skipped_content(sha1_git);
 create unique index on skipped_content(sha256);
 
 -- An organization (or part thereof) that might be in charge of running
 -- software projects. Examples: Debian, GNU, GitHub, Apache, The Linux
 -- Foundation. The data model is hierarchical (via parent_id) and might store
 -- sub-branches of existing organizations. The key feature of an organization
 -- is that it can be *listed* to retrieve information about its content, i.e:
 -- sub-organizations, projects, origins.
 create table organization
 (
   id           bigserial primary key,
   parent_id    bigint references organization(id),
   name         text not null,
   description  text,
   homepage     text,
   list_engine  text,  -- crawler to be used to org's content
   list_url     text,  -- root URL to start the listing
   list_params  json,  -- org-specific listing parameter
   latest_list  timestamptz  -- last time the org's content has been listed
 );
 
 -- Log of all organization listings (i.e., organization crawling) that have
 -- been done in the past, or are still ongoing. Similar to fetch_history, but
 -- for organizations.
 create table list_history
 (
   id           bigserial primary key,
   organization bigint references organization(id),
   date         timestamptz not null,
   status       boolean,  -- true if and only if the listing has been successful
   result       json,     -- more detailed return value, depending on status
   stdout       text,
   stderr       text,
   duration     interval  -- fetch duration of NULL if still ongoing
 );
 
 -- Log of all origin fetches (i.e., origin crawling) that have been done in the
 -- past, or are still ongoing. Similar to list_history, but for origins.
 create table fetch_history
 (
   id        bigserial primary key,
   origin    bigint references origin(id),
   date      timestamptz not null,
   status    boolean,  -- true if and only if the fetch has been successful
   result    json,     -- more detailed returned values, times, etc...
   stdout    text,
   stderr    text,     -- null when status is true, filled otherwise
   duration  interval  -- fetch duration of NULL if still ongoing
 );
 
 -- A specific software project, e.g., the Linux kernel, Apache httpd. A
 -- software project is version-less at this level, but is associated to several
 -- metadata. Metadata can evolve over time, this table only contains the most
 -- recent version of them; for old versions of project see table
 -- project_history.
 create table project
 (
   id            bigserial primary key,
   organization  bigint references organization(id),  -- the "owning" organization
   origin        bigint references origin(id),  -- where to find project releases
   name          text,
   description   text,
   homepage      text,
   doap          jsonb
   -- other kinds of metadata/software project description ontologies can be
   -- added here, in addition to DOAP
 );
 
 -- History of project metadata. Time-sensitive version of the table project.
 create table project_history
 (
   id            bigserial primary key,
   project       bigint references project(id),
   validity      tstzrange,
   organization  bigint references organization(id),
   origin        bigint references origin(id),
   name          text,
   description   text,
   homepage      text,
   doap          jsonb
 );
 
 -- A file-system directory.  A directory is a list of directory entries (see
 -- tables: directory_entry_{dir,file}).
 --
 -- To list the contents of a directory:
 -- 1. list the contained directory_entry_dir using array dir_entries
 -- 2. list the contained directory_entry_file using array file_entries
 -- 3. list the contained directory_entry_rev using array rev_entries
 -- 4. UNION
 --
 -- Synonyms/mappings:
 -- * git: tree
 create table directory
 (
   id            sha1_git primary key,
   dir_entries   bigint[],  -- sub-directories, reference directory_entry_dir
   file_entries  bigint[],  -- contained files, reference directory_entry_file
   rev_entries   bigint[]   -- mounted revisions, reference directory_entry_rev
 );
 
 create index on directory using gin (dir_entries);
 create index on directory using gin (file_entries);
 create index on directory using gin (rev_entries);
 
 -- A directory entry pointing to a sub-directory.
 create table directory_entry_dir
 (
   id      bigserial primary key,
   target  sha1_git,   -- id of target directory
   name    unix_path,  -- path name, relative to containing dir
   perms   file_perms  -- unix-like permissions
 );
 
 create unique index on directory_entry_dir(target, name, perms);
 
 -- A directory entry pointing to a file.
 create table directory_entry_file
 (
   id      bigserial primary key,
   target  sha1_git,   -- id of target file
   name    unix_path,  -- path name, relative to containing dir
   perms   file_perms  -- unix-like permissions
 );
 
 create unique index on directory_entry_file(target, name, perms);
 
 -- A directory entry pointing to a revision.
 create table directory_entry_rev
 (
   id      bigserial primary key,
   target  sha1_git,   -- id of target revision
   name    unix_path,  -- path name, relative to containing dir
   perms   file_perms  -- unix-like permissions
 );
 
 create unique index on directory_entry_rev(target, name, perms);
 
 create table person
 (
   id     bigserial primary key,
   name   text not null default '',
   email  text not null default ''
 );
 
 create unique index on person(name, email);
 
 create type revision_type as enum ('git', 'tar', 'dsc');
 
 -- A snapshot of a software project at a specific point in time.
 --
 -- Synonyms/mappings:
 -- * git / subversion / etc: commit
 -- * tarball: a specific tarball
 --
 -- Revisions are organized as DAGs. Each revision points to 0, 1, or more (in
 -- case of merges) parent revisions. Each revision points to a directory, i.e.,
 -- a file-system tree containing files and directories.
 create table revision
 (
   id                    sha1_git primary key,
   date                  timestamptz,
   date_offset           smallint,
   committer_date        timestamptz,
   committer_date_offset smallint,
   type                  revision_type not null,
   directory             sha1_git,  -- file-system tree
   message               bytea,
   author                bigint references person(id),
   committer             bigint references person(id)
 );
 
 -- either this table or the sha1_git[] column on the revision table
 create table revision_history
 (
   id           sha1_git references revision(id),
   parent_id    sha1_git,
   parent_rank  int not null default 0,
     -- parent position in merge commits, 0-based
   primary key (id, parent_rank)
 );
 
 -- The content of software origins is indexed starting from top-level pointers
 -- called "branches". Every time we fetch some origin we store in this table
 -- where the branches pointed to at fetch time.
 --
 -- Synonyms/mappings:
 -- * git: ref (in the "git update-ref" sense)
 create table occurrence_history
 (
   origin     bigint references origin(id),
   branch     text,  -- e.g., "master" (for VCS), or "sid" (for Debian)
   revision   sha1_git,  -- ref target, e.g., commit id
   authority  bigint references organization(id) not null,
                       -- who is claiming to have seen the occurrence.
                       -- Note: SWH is such an authority, and has an entry in
                       -- the organization table.
   validity   tstzrange,  -- The time validity of this table entry. If the upper
                          -- bound is missing, the entry is still valid.
   exclude using gist (origin with =,
                       branch with =,
                       revision with =,
                       authority with =,
                       validity with &&),
   -- unicity exclusion constraint on lines where the same value is found for
   -- `origin`, `reference`, `revision`, `authority` and overlapping values for
   -- `validity`.
   primary key (origin, branch, revision, authority, validity)
 );
 
 -- Materialized view of occurrence_history, storing the *current* value of each
 -- branch, as last seen by SWH.
 create table occurrence
 (
   origin    bigint references origin(id),
   branch    text,
   revision  sha1_git,
   primary key(origin, branch, revision)
 );
 
 -- A "memorable" point in the development history of a project.
 --
 -- Synonyms/mappings:
 -- * git: tag (of the annotated kind, otherwise they are just references)
 -- * tarball: the release version number
 create table release
 (
   id          sha1_git primary key,
   revision    sha1_git,
   date        timestamptz,
   date_offset smallint,
   name        text,
   comment     bytea,
   author      bigint references person(id)
 );
diff --git a/sql/upgrades/019.sql b/sql/upgrades/019.sql
new file mode 100644
index 00000000..cb7fffeb
--- /dev/null
+++ b/sql/upgrades/019.sql
@@ -0,0 +1,50 @@
+-- SWH DB schema upgrade
+-- from_version: 18
+-- to_version: 19
+-- description: improve performance of swh_{directory,revision,release}_missing
+
+insert into dbversion(version, release, description)
+      values(19, now(), 'Work In Progress');
+
+
+create or replace function swh_directory_missing()
+    returns setof sha1_git
+    language plpgsql
+as $$
+begin
+    return query
+	select id from tmp_directory
+	where not exists (
+	    select 1 from directory d
+	    where d.id = id);
+    return;
+end
+$$;
+
+create or replace function swh_revision_missing()
+    returns setof sha1_git
+    language plpgsql
+as $$
+begin
+    return query
+        select id from tmp_revision
+	where not exists (
+	    select 1 from revision r
+	    where r.id = id);
+    return;
+end
+$$;
+
+create or replace function swh_release_missing()
+    returns setof sha1_git
+    language plpgsql
+as $$
+begin
+    return query
+        select id from tmp_release
+	where not exists (
+	select 1 from release r
+	where r.id = id);
+    return;
+end
+$$;