Add contrib/pg_logicalinspect.

This module provides SQL functions that allow to inspect logical
decoding components.

It currently allows to inspect the contents of serialized logical
snapshots of a running database cluster, which is useful for debugging
or educational purposes.

Author: Bertrand Drouvot
Reviewed-by: Amit Kapila, Shveta Malik, Peter Smith, Peter Eisentraut
Reviewed-by: David G. Johnston
Discussion: https://postgr.es/m/ZscuZ92uGh3wm4tW%40ip-10-97-1-34.eu-west-3.compute.internal

2 files changed, 66 insertions, 39 deletions

diff --git a/src/backend/replication/logical/snapbuild.c b/src/backend/replication/logical/snapbuild.c
index b9df8c0a024..a6a4da32668 100644
--- a/src/backend/replication/logical/snapbuild.c
+++ b/src/backend/replication/logical/snapbuild.c
@@ -1684,34 +1684,31 @@ out:
 }
 
 /*
- * Restore a snapshot into 'builder' if previously one has been stored at the
- * location indicated by 'lsn'. Returns true if successful, false otherwise.
+ * Restore the logical snapshot file contents to 'ondisk'.
+ *
+ * 'context' is the memory context where the catalog modifying/committed xid
+ * will live.
+ * If 'missing_ok' is true, will not throw an error if the file is not found.
  */
-static bool
-SnapBuildRestore(SnapBuild *builder, XLogRecPtr lsn)
+bool
+SnapBuildRestoreSnapshot(SnapBuildOnDisk *ondisk, const char *path,
+						 MemoryContext context, bool missing_ok)
 {
-	SnapBuildOnDisk ondisk;
 	int			fd;
-	char		path[MAXPGPATH];
-	Size		sz;
 	pg_crc32c	checksum;
-
-	/* no point in loading a snapshot if we're already there */
-	if (builder->state == SNAPBUILD_CONSISTENT)
-		return false;
-
-	sprintf(path, "%s/%X-%X.snap",
-			PG_LOGICAL_SNAPSHOTS_DIR,
-			LSN_FORMAT_ARGS(lsn));
+	Size		sz;
 
 	fd = OpenTransientFile(path, O_RDONLY | PG_BINARY);
 
-	if (fd < 0 && errno == ENOENT)
-		return false;
-	else if (fd < 0)
+	if (fd < 0)
+	{
+		if (missing_ok && errno == ENOENT)
+			return false;
+
 		ereport(ERROR,
 				(errcode_for_file_access(),
 				 errmsg("could not open file \"%s\": %m", path)));
+	}
 
 	/* ----
 	 * Make sure the snapshot had been stored safely to disk, that's normally
@@ -1724,47 +1721,46 @@ SnapBuildRestore(SnapBuild *builder, XLogRecPtr lsn)
 	fsync_fname(path, false);
 	fsync_fname(PG_LOGICAL_SNAPSHOTS_DIR, true);
 
-
 	/* read statically sized portion of snapshot */
-	SnapBuildRestoreContents(fd, (char *) &ondisk, SnapBuildOnDiskConstantSize, path);
+	SnapBuildRestoreContents(fd, (char *) ondisk, SnapBuildOnDiskConstantSize, path);
 
-	if (ondisk.magic != SNAPBUILD_MAGIC)
+	if (ondisk->magic != SNAPBUILD_MAGIC)
 		ereport(ERROR,
 				(errcode(ERRCODE_DATA_CORRUPTED),
 				 errmsg("snapbuild state file \"%s\" has wrong magic number: %u instead of %u",
-						path, ondisk.magic, SNAPBUILD_MAGIC)));
+						path, ondisk->magic, SNAPBUILD_MAGIC)));
 
-	if (ondisk.version != SNAPBUILD_VERSION)
+	if (ondisk->version != SNAPBUILD_VERSION)
 		ereport(ERROR,
 				(errcode(ERRCODE_DATA_CORRUPTED),
 				 errmsg("snapbuild state file \"%s\" has unsupported version: %u instead of %u",
-						path, ondisk.version, SNAPBUILD_VERSION)));
+						path, ondisk->version, SNAPBUILD_VERSION)));
 
 	INIT_CRC32C(checksum);
 	COMP_CRC32C(checksum,
-				((char *) &ondisk) + SnapBuildOnDiskNotChecksummedSize,
+				((char *) ondisk) + SnapBuildOnDiskNotChecksummedSize,
 				SnapBuildOnDiskConstantSize - SnapBuildOnDiskNotChecksummedSize);
 
 	/* read SnapBuild */
-	SnapBuildRestoreContents(fd, (char *) &ondisk.builder, sizeof(SnapBuild), path);
-	COMP_CRC32C(checksum, &ondisk.builder, sizeof(SnapBuild));
+	SnapBuildRestoreContents(fd, (char *) &ondisk->builder, sizeof(SnapBuild), path);
+	COMP_CRC32C(checksum, &ondisk->builder, sizeof(SnapBuild));
 
 	/* restore committed xacts information */
-	if (ondisk.builder.committed.xcnt > 0)
+	if (ondisk->builder.committed.xcnt > 0)
 	{
-		sz = sizeof(TransactionId) * ondisk.builder.committed.xcnt;
-		ondisk.builder.committed.xip = MemoryContextAllocZero(builder->context, sz);
-		SnapBuildRestoreContents(fd, (char *) ondisk.builder.committed.xip, sz, path);
-		COMP_CRC32C(checksum, ondisk.builder.committed.xip, sz);
+		sz = sizeof(TransactionId) * ondisk->builder.committed.xcnt;
+		ondisk->builder.committed.xip = MemoryContextAllocZero(context, sz);
+		SnapBuildRestoreContents(fd, (char *) ondisk->builder.committed.xip, sz, path);
+		COMP_CRC32C(checksum, ondisk->builder.committed.xip, sz);
 	}
 
 	/* restore catalog modifying xacts information */
-	if (ondisk.builder.catchange.xcnt > 0)
+	if (ondisk->builder.catchange.xcnt > 0)
 	{
-		sz = sizeof(TransactionId) * ondisk.builder.catchange.xcnt;
-		ondisk.builder.catchange.xip = MemoryContextAllocZero(builder->context, sz);
-		SnapBuildRestoreContents(fd, (char *) ondisk.builder.catchange.xip, sz, path);
-		COMP_CRC32C(checksum, ondisk.builder.catchange.xip, sz);
+		sz = sizeof(TransactionId) * ondisk->builder.catchange.xcnt;
+		ondisk->builder.catchange.xip = MemoryContextAllocZero(context, sz);
+		SnapBuildRestoreContents(fd, (char *) ondisk->builder.catchange.xip, sz, path);
+		COMP_CRC32C(checksum, ondisk->builder.catchange.xip, sz);
 	}
 
 	if (CloseTransientFile(fd) != 0)
@@ -1775,11 +1771,36 @@ SnapBuildRestore(SnapBuild *builder, XLogRecPtr lsn)
 	FIN_CRC32C(checksum);
 
 	/* verify checksum of what we've read */
-	if (!EQ_CRC32C(checksum, ondisk.checksum))
+	if (!EQ_CRC32C(checksum, ondisk->checksum))
 		ereport(ERROR,
 				(errcode(ERRCODE_DATA_CORRUPTED),
 				 errmsg("checksum mismatch for snapbuild state file \"%s\": is %u, should be %u",
-						path, checksum, ondisk.checksum)));
+						path, checksum, ondisk->checksum)));
+
+	return true;
+}
+
+/*
+ * Restore a snapshot into 'builder' if previously one has been stored at the
+ * location indicated by 'lsn'. Returns true if successful, false otherwise.
+ */
+static bool
+SnapBuildRestore(SnapBuild *builder, XLogRecPtr lsn)
+{
+	SnapBuildOnDisk ondisk;
+	char		path[MAXPGPATH];
+
+	/* no point in loading a snapshot if we're already there */
+	if (builder->state == SNAPBUILD_CONSISTENT)
+		return false;
+
+	sprintf(path, "%s/%X-%X.snap",
+			PG_LOGICAL_SNAPSHOTS_DIR,
+			LSN_FORMAT_ARGS(lsn));
+
+	/* validate and restore the snapshot to 'ondisk' */
+	if (!SnapBuildRestoreSnapshot(&ondisk, path, builder->context, true))
+		return false;
 
 	/*
 	 * ok, we now have a sensible snapshot here, figure out if it has more
diff --git a/src/backend/utils/adt/arrayfuncs.c b/src/backend/utils/adt/arrayfuncs.c
index 1640d838852..a715e7e0b8e 100644
--- a/src/backend/utils/adt/arrayfuncs.c
+++ b/src/backend/utils/adt/arrayfuncs.c
@@ -3453,6 +3453,12 @@ construct_array_builtin(Datum *elems, int nelems, Oid elmtype)
 			elmalign = TYPALIGN_SHORT;
 			break;
 
+		case XIDOID:
+			elmlen = sizeof(TransactionId);
+			elmbyval = true;
+			elmalign = TYPALIGN_INT;
+			break;
+
 		default:
 			elog(ERROR, "type %u not supported by construct_array_builtin()", elmtype);
 			/* keep compiler quiet */