This is the
rnd_init() is called when the system wants the storage engine to do a table scan.
Unlike index_init(), rnd_init() can be called two times without rnd_end() in between (it only makes sense if scan=1). then the second call should prepare for the new table scan (e.g if rnd_init allocates the cursor, second call should position it to the start of the table, no need to deallocate and allocate it again
Called from filesort.cc, records.cc, sql_handler.cc, sql_select.cc, sql_table.cc, and sql_update.cc.
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