Introduce a new smgr bulk loading facility.

The new facility makes it easier to optimize bulk loading, as the
logic for buffering, WAL-logging, and syncing the relation only needs
to be implemented once. It's also less error-prone: We have had a
number of bugs in how a relation is fsync'd - or not - at the end of a
bulk loading operation. By centralizing that logic to one place, we
only need to write it correctly once.

The new facility is faster for small relations: Instead of of calling
smgrimmedsync(), we register the fsync to happen at next checkpoint,
which avoids the fsync latency. That can make a big difference if you
are e.g. restoring a schema-only dump with lots of relations.

It is also slightly more efficient with large relations, as the WAL
logging is performed multiple pages at a time. That avoids some WAL
header overhead. The sorted GiST index build did that already, this
moves the buffering to the new facility.

The changes to pageinspect GiST test needs an explanation: Before this
patch, the sorted GiST index build set the LSN on every page to the
special GistBuildLSN value, not the LSN of the WAL record, even though
they were WAL-logged. There was no particular need for it, it just
happened naturally when we wrote out the pages before WAL-logging
them. Now we WAL-log the pages first, like in B-tree build, so the
pages are stamped with the record's real LSN. When the build is not
WAL-logged, we still use GistBuildLSN. To make the test output
predictable, use an unlogged index.

Reviewed-by: Andres Freund
Discussion: https://www.postgresql.org/message-id/30e8f366-58b3-b239-c521-422122dd5150%40iki.fi

1 files changed, 3 insertions, 13 deletions

diff --git a/contrib/pageinspect/sql/gist.sql b/contrib/pageinspect/sql/gist.sql
index d263542ba15..85bc44b8000 100644
--- a/contrib/pageinspect/sql/gist.sql
+++ b/contrib/pageinspect/sql/gist.sql
@@ -1,14 +1,6 @@
--- The gist_page_opaque_info() function prints the page's LSN. Normally,
--- that's constant 1 (GistBuildLSN) on every page of a freshly built GiST
--- index. But with wal_level=minimal, the whole relation is dumped to WAL at
--- the end of the transaction if it's smaller than wal_skip_threshold, which
--- updates the LSNs. Wrap the tests on gist_page_opaque_info() in the
--- same transaction with the CREATE INDEX so that we see the LSNs before
--- they are possibly overwritten at end of transaction.
-BEGIN;
-
--- Create a test table and GiST index.
-CREATE TABLE test_gist AS SELECT point(i,i) p, i::text t FROM
+-- The gist_page_opaque_info() function prints the page's LSN.
+-- Use an unlogged index, so that the LSN is predictable.
+CREATE UNLOGGED TABLE test_gist AS SELECT point(i,i) p, i::text t FROM
     generate_series(1,1000) i;
 CREATE INDEX test_gist_idx ON test_gist USING gist (p);
 
@@ -17,8 +9,6 @@ SELECT * FROM gist_page_opaque_info(get_raw_page('test_gist_idx', 0));
 SELECT * FROM gist_page_opaque_info(get_raw_page('test_gist_idx', 1));
 SELECT * FROM gist_page_opaque_info(get_raw_page('test_gist_idx', 2));
 
-COMMIT;
-
 SELECT * FROM gist_page_items(get_raw_page('test_gist_idx', 0), 'test_gist_idx');
 SELECT * FROM gist_page_items(get_raw_page('test_gist_idx', 1), 'test_gist_idx') LIMIT 5;