MDEV-7850: Optimize Query_log_event::begin_event()

 * Use bfill() to pad a Query_log_event (from GTID event) instead of a loop. * Add error conditions Co-author: Monty <monty@mariadb.org>

Author: bnestere

sql/log_event.cc

@@ -1947,7 +1947,7 @@ Query_log_event::begin_event(String *packet, ulong ev_offset,
  uchar *p= (uchar *)packet->ptr() + ev_offset;
  uchar *q= p + LOG_EVENT_HEADER_LEN;
  size_t data_len= packet->length() - ev_offset;
- size_t dummy_bytes;
+ uint dummy_bytes;
  uint16 flags;
 
  if (checksum_alg == BINLOG_CHECKSUM_ALG_CRC32)
@@ -1975,10 +1975,14 @@ Query_log_event::begin_event(String *packet, ulong ev_offset,
  DUMMY value, and will skip the rest of the status vars section.
  */
  DBUG_ASSERT(data_len >= LOG_EVENT_HEADER_LEN + GTID_HEADER_LEN);
- dummy_bytes= data_len - (LOG_EVENT_HEADER_LEN + GTID_HEADER_LEN);
+ if (data_len < LOG_EVENT_HEADER_LEN + GTID_HEADER_LEN)
+ return 1;
+ DBUG_ASSERT(std::numeric_limits<uint16>::max() >=
+ (data_len - (LOG_EVENT_HEADER_LEN + GTID_HEADER_LEN)));
+ dummy_bytes=
+ static_cast<uint>(data_len - (LOG_EVENT_HEADER_LEN + GTID_HEADER_LEN));
  int2store(q + Q_STATUS_VARS_LEN_OFFSET, dummy_bytes);
- for (size_t i= 0; i < dummy_bytes; i++)
- q[Q_DATA_OFFSET + i]= Q_DUMMY;
+ bfill(&q[Q_DATA_OFFSET], dummy_bytes, Q_DUMMY);
  q[Q_DATA_OFFSET + dummy_bytes]= 0; /* Zero terminator for empty db */
  q+= Q_DATA_OFFSET + dummy_bytes + 1;