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Re: Are some MyISAM settings used for Aria
Le 24/04/2017 à 23:05, Sales a écrit :
On Apr 24, 2017, at 3:04 PM, jocelyn fournier
<jocelyn.fournier@xxxxxxxxx <mailto:jocelyn.fournier@xxxxxxxxx>> wrote:
You should search read_rnd_buff_size, it's used in sql/records.cc
<http://records.cc> to compute the size of the cache_records in the
But, the original link implied use with mrr, however, this page:
"MariaDB uses mrr_buffer_size as a limit of MRR buffer size
for range access, while MySQL uses read_rnd_buffer_size.”
So, I guess it is still used, but, not for mrr.
Yes it's not anymore mrr specific.
The doc from the MariaDB source code is great to understand what it does :
This is a special variant of rr_from_tempfile that can be used for
handlers that is not using the HA_FAST_KEY_READ table flag. Instead
of reading the references one by one from the temporary file it reads
a set of them, sorts them and reads all of them into a buffer which
is then used for a number of subsequent calls to rr_from_cache.
It is only used for SELECT queries and a number of other conditions
on table size.
init_read_record is used to scan by using a number of different methods.
Which method to use is set-up in this call so that later calls to
the info->read_record will call the appropriate method using a function
There are five methods that relate completely to the sort function
filesort. The result of a filesort is retrieved using read_record
calls. The other two methods are used for normal table access.
The filesort will produce references to the records sorted, these
references can be stored in memory or in a temporary file.
The temporary file is normally used when the references doesn't fit into
a properly sized memory buffer. For most small queries the references
are stored in the memory buffer.