Function libpq_executeFileMap

src/bin/pg_rewind/libpq_fetch.c:443–529

* Fetch all changed blocks from remote source data directory. */

 * Fetch all changed blocks from remote source data directory.
 */
void
libpq_executeFileMap(filemap_t *map)
{
	file_entry_t *entry;
	const char *sql;
	PGresult   *res;
	int			i;

	/*
	 * First create a temporary table, and load it with the blocks that we
	 * need to fetch.
	 */
	sql = "CREATE TEMPORARY TABLE fetchchunks(path text, begin int8, len int4);";
	run_simple_command(sql);

	sql = "COPY fetchchunks FROM STDIN";
	res = PQexec(conn, sql);

	if (PQresultStatus(res) != PGRES_COPY_IN)
		pg_fatal("could not send file list: %s",
				 PQresultErrorMessage(res));
	PQclear(res);

	for (i = 0; i < map->narray; i++)
	{
		entry = map->array[i];

		/* If this is a relation file, copy the modified blocks */
		execute_pagemap(&entry->target_pages_to_overwrite, entry->path);

		switch (entry->action)
		{
			case FILE_ACTION_NONE:
				/* nothing else to do */
				break;

			case FILE_ACTION_COPY:
				/* Truncate the old file out of the way, if any */
				open_target_file(entry->path, true);
				fetch_file_range(entry->path, 0, entry->source_size);
				break;

			case FILE_ACTION_TRUNCATE:
				truncate_target_file(entry->path, entry->source_size);
				break;

			case FILE_ACTION_COPY_TAIL:
				fetch_file_range(entry->path, entry->target_size, entry->source_size);
				break;

			case FILE_ACTION_REMOVE:
				remove_target(entry);
				break;

			case FILE_ACTION_CREATE:
				create_target(entry);
				break;