From ade925e1693a595ef1c278583fa699ca6fc1ff45 Mon Sep 17 00:00:00 2001
From: Michael Paquier <michael@paquier.xyz>
Date: Thu, 22 Sep 2022 20:03:30 +0900
Subject: [PATCH] Use min/max bounds defined by Zstd for compression level

The bounds hardcoded in compression.c since ffd5365 (minimum at 1 and
maximum at 22) do not match the reality of what zstd is able to
handle, these values being available via ZSTD_maxCLevel() and
ZSTD_minCLevel() at run-time.  The maximum of 22 is actually correct
in recent versions, but the minimum was not as the library can go down
to -131720 by design.  This commit changes the code to use the run-time
values in the code instead of some hardcoded ones.

Zstd seems to assume that these bounds could change in the future, and
Postgres will be able to adapt automatically to such changes thanks to
what's being done in this commit.

Reported-by: Justin Prysby
Discussion: https://postgr.es/m/20220922033716.GL31833@telsasoft.com
Backpatch-through: 15
---
 doc/src/sgml/protocol.sgml | 6 ++++--
 src/common/compression.c   | 3 ++-
 2 files changed, 6 insertions(+), 3 deletions(-)

diff --git a/doc/src/sgml/protocol.sgml b/doc/src/sgml/protocol.sgml
index 946d5634913..1a70685021d 100644
--- a/doc/src/sgml/protocol.sgml
+++ b/doc/src/sgml/protocol.sgml
@@ -2757,8 +2757,10 @@ psql "dbname=postgres replication=database" -c "IDENTIFY_SYSTEM;"
            <literal>-1</literal>), for <literal>lz4</literal> an integer
            between 1 and 12 (default <literal>0</literal> for fast compression
            mode), and for <literal>zstd</literal> an integer between
-           <literal>1</literal> and <literal>22</literal> (default
-           <literal>ZSTD_CLEVEL_DEFAULT</literal> or <literal>3</literal>).
+           <literal>ZSTD_minCLevel()</literal> (usually <literal>-131072</literal>)
+           and <literal>ZSTD_maxCLevel()</literal> (usually <literal>22</literal>),
+           (default <literal>ZSTD_CLEVEL_DEFAULT</literal> or
+           <literal>3</literal>).
           </para>
 
           <para>
diff --git a/src/common/compression.c b/src/common/compression.c
index e40ce98ef3a..0c6bb9177b9 100644
--- a/src/common/compression.c
+++ b/src/common/compression.c
@@ -324,8 +324,9 @@ validate_compress_specification(pg_compress_specification *spec)
 			default_level = 0;	/* fast mode */
 			break;
 		case PG_COMPRESSION_ZSTD:
-			max_level = 22;
 #ifdef USE_ZSTD
+			max_level = ZSTD_maxCLevel();
+			min_level = ZSTD_minCLevel();
 			default_level = ZSTD_CLEVEL_DEFAULT;
 #endif
 			break;