Fix some issues with WAL segment opening for pg_receivewal --compress

The logic handling the opening of new WAL segments was fuzzy when using
--compress if a partial, non-compressed, segment with the same base name
existed in the repository storing those files.  In this case, using
--compress would cause the code to first check for the existence and the
size of a non-compressed segment, followed by the opening of a new
compressed, partial, segment.  The code was accidentally working
correctly on most platforms as the buildfarm has proved, except
bowerbird where gzflush() could fail in this code path.  It is wrong
anyway to take the code path used pre-padding when creating a new
partial, non-compressed, segment, so let's fix it.

Note that this issue exists when users mix successive runs of
pg_receivewal with or without compression, as discovered with the tests
introduced by ffc9dda.

While on it, this refactors the code so as code paths that need to know
about the ".gz" suffix are down from four to one in walmethods.c, easing
a bit the introduction of new compression methods.  This addresses a
second issue where log messages generated for an unexpected failure
would not show the compressed segment name involved, which was
confusing, printing instead the name of the non-compressed equivalent.

Reported-by: Georgios Kokolatos
Discussion: https://postgr.es/m/YPDLz2x3o1aX2wRh@paquier.xyz
Backpatch-through: 10

diff --git a/src/bin/pg_basebackup/receivelog.c b/src/bin/pg_basebackup/receivelog.c
index 3952a3f94300410480e42ceb453ce28597e0938b..7af90093207b0cf17a3a8db7bc58472e6754bcce 100644 (file)
--- a/src/bin/pg_basebackup/receivelog.c
+++ b/src/bin/pg_basebackup/receivelog.c
@@ -88,26 +88,29 @@ static bool
 open_walfile(StreamCtl *stream, XLogRecPtr startpoint)
 {
        Walfile    *f;
-       char            fn[MAXPGPATH];
+       char       *fn;
        ssize_t         size;
        XLogSegNo       segno;
 
        XLByteToSeg(startpoint, segno, WalSegSz);
        XLogFileName(current_walfile_name, stream->timeline, segno, WalSegSz);
 
-       snprintf(fn, sizeof(fn), "%s%s", current_walfile_name,
-                        stream->partial_suffix ? stream->partial_suffix : "");
+       /* Note that this considers the compression used if necessary */
+       fn = stream->walmethod->get_file_name(current_walfile_name,
+                                                                                 stream->partial_suffix);
 
        /*
         * When streaming to files, if an existing file exists we verify that it's
         * either empty (just created), or a complete WalSegSz segment (in which
         * case it has been created and padded). Anything else indicates a corrupt
-        * file.
+        * file. Compressed files have no need for padding, so just ignore this
+        * case.
         *
         * When streaming to tar, no file with this name will exist before, so we
         * never have to verify a size.
         */
-       if (stream->walmethod->existsfile(fn))
+       if (stream->walmethod->compression() == 0 &&
+               stream->walmethod->existsfile(fn))
        {
                size = stream->walmethod->get_file_size(fn);
                if (size < 0)

diff --git a/src/bin/pg_basebackup/walmethods.c b/src/bin/pg_basebackup/walmethods.c
index a15bbb20e73737aa0a1014488d8a5808f0200dff..09b071b6a4f4cc939360f93f2f0e6c798a47f4ee 100644 (file)
--- a/src/bin/pg_basebackup/walmethods.c
+++ b/src/bin/pg_basebackup/walmethods.c
@@ -68,20 +68,32 @@ dir_getlasterror(void)
        return strerror(errno);
 }
 
+static char *
+dir_get_file_name(const char *pathname, const char *temp_suffix)
+{
+       char       *filename = pg_malloc0(MAXPGPATH * sizeof(char));
+
+       snprintf(filename, MAXPGPATH, "%s%s%s",
+                        pathname, dir_data->compression > 0 ? ".gz" : "",
+                        temp_suffix ? temp_suffix : "");
+
+       return filename;
+}
+
 static Walfile
 dir_open_for_write(const char *pathname, const char *temp_suffix, size_t pad_to_size)
 {
        static char tmppath[MAXPGPATH];
+       char       *filename;
        int                     fd;
        DirectoryMethodFile *f;
 #ifdef HAVE_LIBZ
        gzFile          gzfp = NULL;
 #endif
 
-       snprintf(tmppath, sizeof(tmppath), "%s/%s%s%s",
-                        dir_data->basedir, pathname,
-                        dir_data->compression > 0 ? ".gz" : "",
-                        temp_suffix ? temp_suffix : "");
+       filename = dir_get_file_name(pathname, temp_suffix);
+       snprintf(tmppath, sizeof(tmppath), "%s/%s",
+                        dir_data->basedir, filename);
 
        /*
         * Open a file for non-compressed as well as compressed files. Tracking
@@ -232,26 +244,31 @@ dir_close(Walfile f, WalCloseMethod method)
                /* Build path to the current version of the file */
                if (method == CLOSE_NORMAL && df->temp_suffix)
                {
+                       char       *filename;
+                       char       *filename2;
+
                        /*
                         * If we have a temp prefix, normal operation is to rename the
                         * file.
                         */
-                       snprintf(tmppath, sizeof(tmppath), "%s/%s%s%s",
-                                        dir_data->basedir, df->pathname,
-                                        dir_data->compression > 0 ? ".gz" : "",
-                                        df->temp_suffix);
-                       snprintf(tmppath2, sizeof(tmppath2), "%s/%s%s",
-                                        dir_data->basedir, df->pathname,
-                                        dir_data->compression > 0 ? ".gz" : "");
+                       filename = dir_get_file_name(df->pathname, df->temp_suffix);
+                       snprintf(tmppath, sizeof(tmppath), "%s/%s",
+                                        dir_data->basedir, filename);
+
+                       /* permanent name, so no need for the prefix */
+                       filename2 = dir_get_file_name(df->pathname, NULL);
+                       snprintf(tmppath2, sizeof(tmppath2), "%s/%s",
+                                        dir_data->basedir, filename2);
                        r = durable_rename(tmppath, tmppath2);
                }
                else if (method == CLOSE_UNLINK)
                {
+                       char       *filename;
+
                        /* Unlink the file once it's closed */
-                       snprintf(tmppath, sizeof(tmppath), "%s/%s%s%s",
-                                        dir_data->basedir, df->pathname,
-                                        dir_data->compression > 0 ? ".gz" : "",
-                                        df->temp_suffix ? df->temp_suffix : "");
+                       filename = dir_get_file_name(df->pathname, df->temp_suffix);
+                       snprintf(tmppath, sizeof(tmppath), "%s/%s",
+                                        dir_data->basedir, filename);
                        r = unlink(tmppath);
                }
                else
@@ -313,6 +330,12 @@ dir_get_file_size(const char *pathname)
        return statbuf.st_size;
 }
 
+static int
+dir_compression(void)
+{
+       return dir_data->compression;
+}
+
 static bool
 dir_existsfile(const char *pathname)
 {
@@ -355,6 +378,8 @@ CreateWalDirectoryMethod(const char *basedir, int compression, bool sync)
        method->write = dir_write;
        method->get_current_pos = dir_get_current_pos;
        method->get_file_size = dir_get_file_size;
+       method->get_file_name = dir_get_file_name;
+       method->compression = dir_compression;
        method->close = dir_close;
        method->sync = dir_sync;
        method->existsfile = dir_existsfile;
@@ -527,11 +552,22 @@ tar_write_padding_data(TarMethodFile *f, size_t bytes)
        return true;
 }
 
+static char *
+tar_get_file_name(const char *pathname, const char *temp_suffix)
+{
+       char       *filename = pg_malloc0(MAXPGPATH * sizeof(char));
+
+       snprintf(filename, MAXPGPATH, "%s%s",
+                        pathname, temp_suffix ? temp_suffix : "");
+
+       return filename;
+}
+
 static Walfile
 tar_open_for_write(const char *pathname, const char *temp_suffix, size_t pad_to_size)
 {
        int                     save_errno;
-       static char tmppath[MAXPGPATH];
+       char       *tmppath;
 
        tar_clear_error();
 
@@ -583,8 +619,7 @@ tar_open_for_write(const char *pathname, const char *temp_suffix, size_t pad_to_
 
        tar_data->currentfile = pg_malloc0(sizeof(TarMethodFile));
 
-       snprintf(tmppath, sizeof(tmppath), "%s%s",
-                        pathname, temp_suffix ? temp_suffix : "");
+       tmppath = tar_get_file_name(pathname, temp_suffix);
 
        /* Create a header with size set to 0 - we will fill out the size on close */
        if (tarCreateHeader(tar_data->currentfile->header, tmppath, NULL, 0, S_IRUSR | S_IWUSR, 0, 0, time(NULL)) != TAR_OK)
@@ -689,6 +724,12 @@ tar_get_file_size(const char *pathname)
        return -1;
 }
 
+static int
+tar_compression(void)
+{
+       return tar_data->compression;
+}
+
 static off_t
 tar_get_current_pos(Walfile f)
 {
@@ -994,6 +1035,8 @@ CreateWalTarMethod(const char *tarbase, int compression, bool sync)
        method->write = tar_write;
        method->get_current_pos = tar_get_current_pos;
        method->get_file_size = tar_get_file_size;
+       method->get_file_name = tar_get_file_name;
+       method->compression = tar_compression;
        method->close = tar_close;
        method->sync = tar_sync;
        method->existsfile = tar_existsfile;

diff --git a/src/bin/pg_basebackup/walmethods.h b/src/bin/pg_basebackup/walmethods.h
index fc4bb52cb742c17a6a39e55bb681dbd23bdebb9b..8d7f24f9e14694c13599ff1f3568d6a99af4dfc3 100644 (file)
--- a/src/bin/pg_basebackup/walmethods.h
+++ b/src/bin/pg_basebackup/walmethods.h
@@ -52,6 +52,15 @@ struct WalWriteMethod
        /* Return the size of a file, or -1 on failure. */
        ssize_t         (*get_file_size) (const char *pathname);
 
+       /*
+        * Return the name of the current file to work on, without the base
+        * directory.  This is useful for logging.
+        */
+       char       *(*get_file_name) (const char *pathname, const char *temp_suffix);
+
+       /* Return the level of compression */
+       int                     (*compression) (void);
+
        /*
         * Write count number of bytes to the file, and return the number of bytes
         * actually written or -1 for error.