Feedback-ID: i0fe9450f:Fastmail
Date: Tue, 29 Nov 2022 15:19:17 +0900
From: Michael Paquier <michael@paquier.xyz>
To: gkokolatos@pm.me
Cc: Justin Pryzby <pryzby@telsasoft.com>,
	pgsql-hackers@lists.postgresql.org,
	Rachel Heaton <rachelmheaton@gmail.com>
Subject: Re: Add LZ4 compression in pg_dump
Message-ID: <Y4WkZUGkic9jWb5I@paquier.xyz>
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On Mon, Nov 28, 2022 at 04:32:43PM +0000, gkokolatos@pm.me wrote:
> The focus of this version of this series is 0001 and 0002.
>=20
> Admittedly 0001 could be presented in a separate thread though given its =
size and
> proximity to the topic, I present it here.

I don't mind.  This was a hole in meson.build, so nice catch!  I have
noticed a second defect with pg_verifybackup for all the commands, and
applied both at the same time.

> In an earlier review you spotted the similarity between pg_dump's and pg_=
receivewal's
> parsing of compression options. However there exists a substantial differ=
ence in the
> behaviour of the two programs; one treats the lack of support for the req=
uested
> algorithm as a fatal error, whereas the other does not. The existing func=
tions in
> common/compression.c do not account for the later. 0002 proposes an imple=
mentation
> for this. It's usefulness is shown in 0003.

In what does it matter?  The logic in compression.c provides an error
when looking at a spec or validating it, but the caller is free to
consume it as it wants because this is shared between the frontend and
the backend, and that includes consuming it as a warning rather than a
ahrd failure.  If we don't want to issue an error and force
non-compression if attempting to use a compression method not
supported in pg_dump, that's fine by me as a historical behavior, but
I don't see why these routines have any need to be split more as
proposed in 0002.

Saying that, I do agree that it would be nice to remove the
duplication between the option parsing of pg_basebackup and
pg_receivewal.  Your patch is very close to that, actually, and it
occured to me that if we move the check on "server-" and "client-" in
pg_basebackup to be just before the integer-only check then we can
consolidate the whole thing.

Attached is an alternative that does not sacrifice the pluggability of
the existing routines while allowing 0003~ to still use them (I don't
really want to move around the checks on the supported build options
now in parse_compress_specification(), that was hard enough to settle
on this location).  On top of that, pg_basebackup is able to cope with
the case of --compress=3D0 already, enforcing "none" (BaseBackup could
be simplified a bit more before StartLogStreamer).  This refactoring
shaves a little bit of code.

> Please consider 0003-0005 as work in progress. They are differences from =
v7 yet they
> may contain unaddressed comments for now.

Okay.
--
Michael

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=46rom 6fb2aa609348ad7df6f9c12da60c07aa96243965 Mon Sep 17 00:00:00 2001
=46rom: Michael Paquier <michael@paquier.xyz>
Date: Tue, 29 Nov 2022 15:17:27 +0900
Subject: [PATCH v9] Make the pg_receivewal compression parsing function com=
mon

Also and relax parsing errors in the helper functions and re-introduce thos=
e as
an independed function.

As it is shown in the rest of the patch series, there is a lot of duplicati=
on
between pg_dump's parsing of compression options and pg_receivewal's. Now t=
he
core work is done in common. However pg_dump would not error out if the
requested compression algorithm is not supported by the build, whereas other
callers will error out. Also it seems a bit weird for only one of the parsi=
ng
functions for compressions to error out on missing support and that one to =
not
be the one responsible for identifying the compression algorithm.

A new function is added to test the support of the algorithm allowing the u=
ser
to tune the behaviour.
---
 src/include/common/compression.h      |  2 +
 src/common/compression.c              | 63 +++++++++++++++++++++++++++
 src/bin/pg_basebackup/pg_basebackup.c | 49 ++++-----------------
 src/bin/pg_basebackup/pg_receivewal.c | 61 --------------------------
 4 files changed, 73 insertions(+), 102 deletions(-)

diff --git a/src/include/common/compression.h b/src/include/common/compress=
ion.h
index 5d680058ed..46855b1a3b 100644
--- a/src/include/common/compression.h
+++ b/src/include/common/compression.h
@@ -33,6 +33,8 @@ typedef struct pg_compress_specification
 	char	   *parse_error;	/* NULL if parsing was OK, else message */
 } pg_compress_specification;
=20
+extern void parse_compress_options(const char *option, char **algorithm,
+								   char **detail);
 extern bool parse_compress_algorithm(char *name, pg_compress_algorithm *al=
gorithm);
 extern const char *get_compress_algorithm_name(pg_compress_algorithm algor=
ithm);
=20
diff --git a/src/common/compression.c b/src/common/compression.c
index df5b627834..5274ba5ba8 100644
--- a/src/common/compression.c
+++ b/src/common/compression.c
@@ -356,3 +356,66 @@ validate_compress_specification(pg_compress_specificat=
ion *spec)
=20
 	return NULL;
 }
+
+#ifdef FRONTEND
+
+/*
+ * Basic parsing of a value specified through a command-line option, commo=
nly
+ * -Z/--compress.
+ *
+ * The parsing consists of a METHOD:DETAIL string fed later to
+ * parse_compress_specification().  This only extracts METHOD and DETAIL.
+ * If only an integer is found, the method is implied by the value specifi=
ed.
+ */
+void
+parse_compress_options(const char *option, char **algorithm, char **detail)
+{
+	char	   *sep;
+	char	   *endp;
+	long		result;
+
+	/*
+	 * Check whether the compression specification consists of a bare integer.
+	 *
+	 * For backward-compatibility, assume "none" if the integer found is zero
+	 * and "gzip" otherwise.
+	 */
+	result =3D strtol(option, &endp, 10);
+	if (*endp =3D=3D '\0')
+	{
+		if (result =3D=3D 0)
+		{
+			*algorithm =3D pstrdup("none");
+			*detail =3D NULL;
+		}
+		else
+		{
+			*algorithm =3D pstrdup("gzip");
+			*detail =3D pstrdup(option);
+		}
+		return;
+	}
+
+	/*
+	 * Check whether there is a compression detail following the algorithm
+	 * name.
+	 */
+	sep =3D strchr(option, ':');
+	if (sep =3D=3D NULL)
+	{
+		*algorithm =3D pstrdup(option);
+		*detail =3D NULL;
+	}
+	else
+	{
+		char	   *alg;
+
+		alg =3D palloc((sep - option) + 1);
+		memcpy(alg, option, sep - option);
+		alg[sep - option] =3D '\0';
+
+		*algorithm =3D alg;
+		*detail =3D pstrdup(sep + 1);
+	}
+}
+#endif	/* FRONTEND */
diff --git a/src/bin/pg_basebackup/pg_basebackup.c b/src/bin/pg_basebackup/=
pg_basebackup.c
index 22836ca01a..4f56c9f464 100644
--- a/src/bin/pg_basebackup/pg_basebackup.c
+++ b/src/bin/pg_basebackup/pg_basebackup.c
@@ -956,27 +956,13 @@ parse_max_rate(char *src)
  * at a later stage.
  */
 static void
-parse_compress_options(char *option, char **algorithm, char **detail,
-					   CompressionLocation *locationres)
+backup_parse_compress_options(char *option, char **algorithm, char **detai=
l,
+							  CompressionLocation *locationres)
 {
-	char	   *sep;
-	char	   *endp;
-
 	/*
-	 * Check whether the compression specification consists of a bare integer.
-	 *
-	 * If so, for backward compatibility, assume gzip.
+	 * Strip off any "client-" or "server-" prefix, calculating the
+	 * location.
 	 */
-	(void) strtol(option, &endp, 10);
-	if (*endp =3D=3D '\0')
-	{
-		*locationres =3D COMPRESS_LOCATION_UNSPECIFIED;
-		*algorithm =3D pstrdup("gzip");
-		*detail =3D pstrdup(option);
-		return;
-	}
-
-	/* Strip off any "client-" or "server-" prefix. */
 	if (strncmp(option, "server-", 7) =3D=3D 0)
 	{
 		*locationres =3D COMPRESS_LOCATION_SERVER;
@@ -990,27 +976,8 @@ parse_compress_options(char *option, char **algorithm,=
 char **detail,
 	else
 		*locationres =3D COMPRESS_LOCATION_UNSPECIFIED;
=20
-	/*
-	 * Check whether there is a compression detail following the algorithm
-	 * name.
-	 */
-	sep =3D strchr(option, ':');
-	if (sep =3D=3D NULL)
-	{
-		*algorithm =3D pstrdup(option);
-		*detail =3D NULL;
-	}
-	else
-	{
-		char	   *alg;
-
-		alg =3D palloc((sep - option) + 1);
-		memcpy(alg, option, sep - option);
-		alg[sep - option] =3D '\0';
-
-		*algorithm =3D alg;
-		*detail =3D pstrdup(sep + 1);
-	}
+	/* fallback to the common parsing for the algorithm and detail */
+	parse_compress_options(option, algorithm, detail);
 }
=20
 /*
@@ -2411,8 +2378,8 @@ main(int argc, char **argv)
 				compressloc =3D COMPRESS_LOCATION_UNSPECIFIED;
 				break;
 			case 'Z':
-				parse_compress_options(optarg, &compression_algorithm,
-									   &compression_detail, &compressloc);
+				backup_parse_compress_options(optarg, &compression_algorithm,
+											  &compression_detail, &compressloc);
 				break;
 			case 'c':
 				if (pg_strcasecmp(optarg, "fast") =3D=3D 0)
diff --git a/src/bin/pg_basebackup/pg_receivewal.c b/src/bin/pg_basebackup/=
pg_receivewal.c
index 63207ca025..c7a46b8a2a 100644
--- a/src/bin/pg_basebackup/pg_receivewal.c
+++ b/src/bin/pg_basebackup/pg_receivewal.c
@@ -57,8 +57,6 @@ static XLogRecPtr endpos =3D InvalidXLogRecPtr;
=20
=20
 static void usage(void);
-static void parse_compress_options(char *option, char **algorithm,
-								   char **detail);
 static DIR *get_destination_dir(char *dest_folder);
 static void close_destination_dir(DIR *dest_dir, char *dest_folder);
 static XLogRecPtr FindStreamingStart(uint32 *tli);
@@ -109,65 +107,6 @@ usage(void)
 	printf(_("%s home page: <%s>\n"), PACKAGE_NAME, PACKAGE_URL);
 }
=20
-/*
- * Basic parsing of a value specified for -Z/--compress
- *
- * The parsing consists of a METHOD:DETAIL string fed later on to a more
- * advanced routine in charge of proper validation checks.  This only extr=
acts
- * METHOD and DETAIL.  If only an integer is found, the method is implied =
by
- * the value specified.
- */
-static void
-parse_compress_options(char *option, char **algorithm, char **detail)
-{
-	char	   *sep;
-	char	   *endp;
-	long		result;
-
-	/*
-	 * Check whether the compression specification consists of a bare integer.
-	 *
-	 * For backward-compatibility, assume "none" if the integer found is zero
-	 * and "gzip" otherwise.
-	 */
-	result =3D strtol(option, &endp, 10);
-	if (*endp =3D=3D '\0')
-	{
-		if (result =3D=3D 0)
-		{
-			*algorithm =3D pstrdup("none");
-			*detail =3D NULL;
-		}
-		else
-		{
-			*algorithm =3D pstrdup("gzip");
-			*detail =3D pstrdup(option);
-		}
-		return;
-	}
-
-	/*
-	 * Check whether there is a compression detail following the algorithm
-	 * name.
-	 */
-	sep =3D strchr(option, ':');
-	if (sep =3D=3D NULL)
-	{
-		*algorithm =3D pstrdup(option);
-		*detail =3D NULL;
-	}
-	else
-	{
-		char	   *alg;
-
-		alg =3D palloc((sep - option) + 1);
-		memcpy(alg, option, sep - option);
-		alg[sep - option] =3D '\0';
-
-		*algorithm =3D alg;
-		*detail =3D pstrdup(sep + 1);
-	}
-}
=20
 /*
  * Check if the filename looks like a WAL file, letting caller know if this
--=20
2.38.1


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