From: Heikki Linnakangas <heikki.linnakangas@iki.fi>
Date: Fri, 16 Jan 2015 12:16:18 +0000 (+0200)
Subject: Improve comments.
X-Git-Url: http://git.postgresql.org/gitweb/static/tut_user.html?a=commitdiff_plain;h=8d232649c7ccc75d6454598d5ba1ab4af2102041;p=users%2Fheikki%2Fpostgres.git

Improve comments.

Move comments out of SQL queries, into the surrounding code.
---

diff --git a/src/bin/pg_rewind/libpq_fetch.c b/src/bin/pg_rewind/libpq_fetch.c
index 57cb6a6e70..dc1ecdd89e 100644
--- a/src/bin/pg_rewind/libpq_fetch.c
+++ b/src/bin/pg_rewind/libpq_fetch.c
@@ -32,7 +32,11 @@
 static PGconn *conn = NULL;
 
 /*
- * Relation files are fetched max CHUNKSIZE bytes at a time.
+ * Files are fetched max CHUNKSIZE bytes at a time.
+ *
+ * (This only applies to files that are copied in whole, or for truncated
+ * files where we copy the tail. Relation files, where we know the individual
+ * blocks that need to be fetched, are fetched in BLCKSZ chunks.)
  */
 #define CHUNKSIZE 1000000
 
@@ -131,8 +135,17 @@ libpqProcessFileList(void)
 	const char *sql;
 	int			i;
 
+	/*
+	 * Create a recursive directory listing of the whole data directory.
+	 *
+	 * The WITH RECURSIVE part does most of the work. The second part
+	 * gets the targets of the symlinks in pg_tblspc directory.
+	 *
+	 * XXX: There is no backend function to get a symbolic link's target in
+	 * general, so if the admin has put any custom symbolic links in the data
+	 * directory, they won't be copied correctly.
+	 */
 	sql =
-		"-- Create a recursive directory listing of the whole data directory\n"
 		"WITH RECURSIVE files (path, filename, size, isdir) AS (\n"
 		"  SELECT '' AS path, filename, size, isdir FROM\n"
 		"  (SELECT pg_ls_dir('.') AS filename) AS fn,\n"
@@ -145,13 +158,6 @@ libpqProcessFileList(void)
 		"       pg_stat_file(parent.path || parent.filename || '/' || fn) AS this\n"
 		"       WHERE parent.isdir = 't'\n"
 		")\n"
-		"-- Using the cte, fetch a listing of the all the files.\n"
-		"--\n"
-		"-- For tablespaces, use pg_tablespace_location() function to fetch\n"
-		"-- the link target (there is no backend function to get a symbolic\n"
-		"-- link's target in general, so if the admin has put any custom\n"
-		"-- symbolic links in the data directory, they won't be copied\n"
-		"-- correctly)\n"
 		"SELECT path || filename, size, isdir,\n"
 		"       pg_tablespace_location(pg_tablespace.oid) AS link_target\n"
 		"FROM files\n"
@@ -420,9 +426,11 @@ libpq_executeFileMap(filemap_t *map)
 					 PQresultErrorMessage(res));
 	}
 
-	/* Ok, we've sent the file list. Now receive the files. */
+	/*
+	 * We've now copied the list of file ranges that we need to fetch to
+	 * the temporary table. Now, actually fetch all of those ranges.
+	 */
 	sql =
-		"-- fetch all the blocks listed in the temp table.\n"
 		"SELECT path, begin, \n"
 		"  pg_read_binary_file(path, begin, len) AS chunk\n"
 		"FROM fetchchunks\n";
@@ -430,7 +438,6 @@ libpq_executeFileMap(filemap_t *map)
 	receiveFileChunks(sql);
 }
 
-
 static void
 execute_pagemap(datapagemap_t *pagemap, const char *path)
 {