diff options
Diffstat (limited to 'src/bin/pg_rewind/libpq_source.c')
| -rw-r--r-- | src/bin/pg_rewind/libpq_source.c | 32 |
1 files changed, 32 insertions, 0 deletions
diff --git a/src/bin/pg_rewind/libpq_source.c b/src/bin/pg_rewind/libpq_source.c index 997d4e2b482..011c9cce6eb 100644 --- a/src/bin/pg_rewind/libpq_source.c +++ b/src/bin/pg_rewind/libpq_source.c @@ -63,6 +63,7 @@ static void process_queued_fetch_requests(libpq_source *src); /* public interface functions */ static void libpq_traverse_files(rewind_source *source, process_file_callback_t callback); +static void libpq_queue_fetch_file(rewind_source *source, const char *path, size_t len); static void libpq_queue_fetch_range(rewind_source *source, const char *path, off_t off, size_t len); static void libpq_finish_fetch(rewind_source *source); @@ -88,6 +89,7 @@ init_libpq_source(PGconn *conn) src->common.traverse_files = libpq_traverse_files; src->common.fetch_file = libpq_fetch_file; + src->common.queue_fetch_file = libpq_queue_fetch_file; src->common.queue_fetch_range = libpq_queue_fetch_range; src->common.finish_fetch = libpq_finish_fetch; src->common.get_current_wal_insert_lsn = libpq_get_current_wal_insert_lsn; @@ -308,6 +310,36 @@ libpq_traverse_files(rewind_source *source, process_file_callback_t callback) } /* + * Queue up a request to fetch a file from remote system. + */ +static void +libpq_queue_fetch_file(rewind_source *source, const char *path, size_t len) +{ + /* + * Truncate the target file immediately, and queue a request to fetch it + * from the source. If the file is small, smaller than MAX_CHUNK_SIZE, + * request fetching a full-sized chunk anyway, so that if the file has + * become larger in the source system, after we scanned the source + * directory, we still fetch the whole file. This only works for files up + * to MAX_CHUNK_SIZE, but that's good enough for small configuration files + * and such that are changed every now and then, but not WAL-logged. For + * larger files, we fetch up to the original size. + * + * Even with that mechanism, there is an inherent race condition if the + * file is modified at the same instant that we're copying it, so that we + * might copy a torn version of the file with one half from the old + * version and another half from the new. But pg_basebackup has the same + * problem, and it hasn't been a problem in practice. + * + * It might seem more natural to truncate the file later, when we receive + * it from the source server, but then we'd need to track which + * fetch-requests are for a whole file. + */ + open_target_file(path, true); + libpq_queue_fetch_range(source, path, 0, Max(len, MAX_CHUNK_SIZE)); +} + +/* * Queue up a request to fetch a piece of a file from remote system. */ static void |