Support pg17

[kathia-barahona]

About this change - What it does

Includes necessary changes for supporting PostgreSQL 17.

This PR updates the behavior of pg_walfile_name based on changes introduced in PostgreSQL 17 (PG17). Instead of calling `(pg_current_lsn), the function now uses the LSN obtained from the result of pg_backup_stop.

Why this way

For versions earlier than PG17, pg_walfile_name returns the previous WAL file name in certain edge cases, such as when the backup’s ending LSN falls on a segment boundary. This issue was resolved in PG17, making the get_backup_end_segment_and_time function largely obsolete for newer versions. As a result, for PG17 and later, backup end segments now rely directly on the pg_backup_stop result.

Note on Testing
While an edge case test was considered (where the backup’s ending LSN falls on a boundary), it was ultimately not included. This test requires a fresh PostgreSQL service to reliably reproduce the scenario. However, in shared pipeline environments, where other tests may have already committed transactions, reproducing the issue is highly inconsistent. Therefore, the test was deemed impractical for inclusion.

class TestPGBaseBackup:
        def test_backup_end_segment_and_time(self, db, pg_version: str):
        conn = db.connect()
        conn.autocommit = True
        cursor = conn.cursor()

        # Force a WAL switch to guarantee that the next LSN is at the start of a new WAL segment
        cursor.execute("SELECT pg_switch_wal();")

        # Generate enough activity to ensure we approach a segment boundary (16 MB)
        cursor.execute("DROP TABLE IF EXISTS wal_test;")
        cursor.execute("CREATE TABLE wal_test (id serial, data text);")
        for _ in range(1024):
            cursor.execute("INSERT INTO wal_test (data) SELECT 'x' || repeat('y', 1024) FROM generate_series(1, 1024);")
        cursor.execute("CHECKPOINT;")
        cursor.execute("SELECT pg_switch_wal();")

        # basic PGBaseBackup, just use backup_end_segment_and_time for noticing discrepancies among versions
        # when LSN falls on a boundary

        pgb = PGBaseBackup(
            config=SIMPLE_BACKUP_CONFIG,
            site="foosite",
            connection_info=None,
            basebackup_path=None,
            compression_queue=None,
            storage=None,
            transfer_queue=None,
            metrics=metrics.Metrics(statsd={}),
            pg_version_server=int(pg_version) * 10000,
        )

        basebackup_name = "test_backup"

        # Manually start and stop backup (could be better, but just need to test basic behavior)
        # pylint: disable=protected-access
        pgb._start_backup(cursor, basebackup_name)
        stop_backup_result = pgb._stop_backup(cursor)

        expected_segment = self._calculate_wal_segment(lsn=stop_backup_result.lsn)

        # for >=PG17 must rely on stop_backup_result LSN, not on current_lsn. For demo this,
        # will change pg_version_server to PG16 and show what will happen if fix in pg_walfile_name is not considered
        if int(pg_version) >= 17:
            pgb.pg_version_server = 160000
            result_end_segment, _ = pgb.get_backup_end_segment_and_time(stop_backup_result, conn)
            assert result_end_segment != expected_segment  # relying on steps for <PG17, is not accurate.

            # set back and test again
            pgb.pg_version_server = int(pg_version) * 10000

        result_end_segment, _ = pgb.get_backup_end_segment_and_time(stop_backup_result, conn)
        assert result_end_segment == expected_segment

    def _calculate_wal_segment(self, lsn: str, timeline: str = "00000001") -> str:
        # Extract XLog ID and Offset from LSN (format: XLogID/Offset)
        xlog_id, xlog_offset = map(lambda x: int(x, 16), lsn.split("/"))

        # Calculate the WAL segment number
        segment_number = (xlog_id << 32 | xlog_offset) // 0x01000000

        # Format the segment number into XLog ID and Offset
        xlog_id_formatted = f"{segment_number >> 32:08X}"
        xlog_offset_formatted = f"{segment_number & 0xFFFFFFFF:08X}"

        return f"{timeline}{xlog_id_formatted}{xlog_offset_formatted}"

Resolves: #BF-2568

UPDATE:

Decided to remove changes in get_backup_end_segment_and_time for considering changes in pg_walfile_name for PG17, was discussed offline and we agreed to keep old behavior rather than having two different ways for getting the end segment.