Use unlogged build for gist_indexsortbuild_flush_ready_pages (#11753)

## Problem

See https://github.com/neondatabase/neon/issues/11718

GIST index can be constructed in two ways: GIST_SORTED_BUILD and
GIST_BUFFERING.
We used unlogged build in the second case but not in the first.

## Summary of changes

Use unlogged build in `gist_indexsortbuild_flush_ready_pages`

Correspondent Postgres PRsL:
https://github.com/neondatabase/postgres/pull/624
https://github.com/neondatabase/postgres/pull/625
https://github.com/neondatabase/postgres/pull/626

---------

Co-authored-by: Konstantin Knizhnik <knizhnik@neon.tech>
Co-authored-by: Heikki Linnakangas <heikki@neon.tech>

pgxn/neon/pagestore_smgr.c

@@ -1989,8 +1989,14 @@ neon_start_unlogged_build(SMgrRelation reln)
 			neon_log(ERROR, "unknown relpersistence '%c'", reln->smgr_relpersistence);
 	}
 
+#if PG_MAJORVERSION_NUM >= 17
+	/*
+	 * We have to disable this check for pg14-16 because sorted build of GIST index requires
+	 * to perform unlogged build several times
+	 */
 	if (smgrnblocks(reln, MAIN_FORKNUM) != 0)
 		neon_log(ERROR, "cannot perform unlogged index build, index is not empty ");
+#endif
 
 	unlogged_build_rel = reln;
 	unlogged_build_phase = UNLOGGED_BUILD_PHASE_1;

test_runner/regress/test_gist.py

@@ -0,0 +1,28 @@
+from __future__ import annotations
+
+from typing import TYPE_CHECKING
+
+if TYPE_CHECKING:
+    from fixtures.neon_fixtures import NeonEnv
+
+
+#
+# Test unlogged build for GIST index
+#
+def test_gist(neon_simple_env: NeonEnv):
+    env = neon_simple_env
+    endpoint = env.endpoints.create_start("main")
+    con = endpoint.connect()
+    cur = con.cursor()
+    iterations = 100
+
+    for _ in range(iterations):
+        cur.execute(
+            "CREATE TABLE pvactst (i INT, a INT[], p POINT) with (autovacuum_enabled = off)"
+        )
+        cur.execute(
+            "INSERT INTO pvactst SELECT i, array[1,2,3], point(i, i+1) FROM generate_series(1,1000) i"
+        )
+        cur.execute("CREATE INDEX gist_pvactst ON pvactst USING gist (p)")
+        cur.execute("VACUUM pvactst")
+        cur.execute("DROP TABLE pvactst")

vendor/revisions.json

@@ -5,14 +5,14 @@
   ],
   "v16": [
     "16.8",
-    "37496f87b5324af53c56127e278ee5b1e8435253"
+    "05ddf212e2e07b788b5c8b88bdcf98630941f6ae"
   ],
   "v15": [
     "15.12",
-    "8ecb12f21d862dfa39f7204b8f5e1c00a2a225b3"
+    "b838c8969b7c63f3e637a769656f5f36793b797c"
   ],
   "v14": [
     "14.17",
-    "d3c9d61fb7a362a165dac7060819dd9d6ad68c28"
+    "c8dab02bfc003ae7bd59096919042d7840f3c194"
   ]
 }