Hi!
On Fri, Aug 25, 2023 at 10:16 AM Kristian Nielsen
<kniel...@knielsen-hq.org> wrote:
>
> Preparatory patch for pre-computing binlog checksums outside of holding
> LOCK_log.
>
> The existing code for MYSQL_BIN_LOG::write_cache() was needlessly complex
> and very hard to understand and modify for handling the new case where
> pre-computed checksums are already present in the IO_CACHE.
MDEV-31273: Refactor MYSQL_BIN_LOG::write_cache()
> if (likely(length > LOG_EVENT_HEADER_LEN))
> {
> header= cache->read_pos;
> cache->read_pos+= LOG_EVENT_HEADER_LEN;
> length-= LOG_EVENT_HEADER_LEN;
> }
> else
> {
> size_t sofar= length;
> size_t remain= LOG_EVENT_HEADER_LEN - sofar;
> header= &header_buf[0];
> memcpy(header, cache->read_pos, sofar);
> cache->read_pos+= sofar;
>
> while (hdr_offs < length)
> length= my_b_fill(cache);
> if (!length)
> goto error_in_read;
> size_t chunk= std::min(length, remain);
> memcpy(header + sofar, cache->read_pos, chunk);
> sofar+= chunk;
> remain-= chunk;
> cache->read_pos+= chunk;
> length-= chunk;
> } while (unlikely(remain > 0));
> }
>
The above can be replaced with:
if (my_b_read(cache, header, LOG_EVENT_HEAD_LENGTH))
goto error_in_read;
It is almost exactly as efficent as the above (one extra if) and avoids using
cache internals.
Note that you do not have to do call my_fill() if you use my_b_read().
my_b_read() will return 0 if it was able to read all data.
In case of end of file, my_b_read() will return 1 and info->error will be 0.
If needed, you can als find out how much data left to read from IO_CACHE:
left_data_to_read= (cache->end_of_file - my_b_tell(cache))
(I can make an inline function of that if needed).
/* Write the rest of the event. */
> while (ev_len > 0)
> {
> if (length == 0)
> length= my_b_fill(cache);
> if (!length)
> goto error_in_read;
>
->
while (ev_len > 0)
{
if (length == 0)
{
if (!(length= my_b_fill(cache)));
goto error_in_read;
}
<cut>
uint chunk= std::min(ev_len, (uint)length);
I would have prefer to have MY_MIN() used (like the rest of the code).
(not critical)
Regards,
Monty
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