diff options
Diffstat (limited to 'storage/innodb_plugin/buf/buf0rea.c')
| -rw-r--r-- | storage/innodb_plugin/buf/buf0rea.c | 170 |
1 files changed, 170 insertions, 0 deletions
diff --git a/storage/innodb_plugin/buf/buf0rea.c b/storage/innodb_plugin/buf/buf0rea.c index 81f788baac2..0b36eeb5cd3 100644 --- a/storage/innodb_plugin/buf/buf0rea.c +++ b/storage/innodb_plugin/buf/buf0rea.c @@ -38,6 +38,14 @@ Created 11/5/1995 Heikki Tuuri #include "srv0start.h" #include "srv0srv.h" +/** The size in blocks of the area where the random read-ahead algorithm counts +the accessed pages when deciding whether to read-ahead */ +#define BUF_READ_AHEAD_RANDOM_AREA BUF_READ_AHEAD_AREA + +/** There must be at least this many pages in buf_pool in the area to start +a random read-ahead */ +#define BUF_READ_AHEAD_RANDOM_THRESHOLD (5 + BUF_READ_AHEAD_RANDOM_AREA / 8) + /** The linear read-ahead area size */ #define BUF_READ_AHEAD_LINEAR_AREA BUF_READ_AHEAD_AREA @@ -158,6 +166,165 @@ buf_read_page_low( } /********************************************************************//** +Applies a random read-ahead in buf_pool if there are at least a threshold +value of accessed pages from the random read-ahead area. Does not read any +page, not even the one at the position (space, offset), if the read-ahead +mechanism is not activated. NOTE 1: the calling thread may own latches on +pages: to avoid deadlocks this function must be written such that it cannot +end up waiting for these latches! NOTE 2: the calling thread must want +access to the page given: this rule is set to prevent unintended read-aheads +performed by ibuf routines, a situation which could result in a deadlock if +the OS does not support asynchronous i/o. +@return number of page read requests issued; NOTE that if we read ibuf +pages, it may happen that the page at the given page number does not +get read even if we return a positive value! */ +static +ulint +buf_read_ahead_random( +/*==================*/ + ulint space, /*!< in: space id */ + ulint zip_size,/*!< in: compressed page size in bytes, or 0 */ + ulint offset) /*!< in: page number of a page which the current thread + wants to access */ +{ + ib_int64_t tablespace_version; + ulint recent_blocks = 0; + ulint count; + ulint ibuf_mode; + ulint low, high; + ulint err; + ulint i; + ulint buf_read_ahead_random_area; + + if (!srv_random_read_ahead) { + /* Disabled by user */ + return(0); + } + + if (srv_startup_is_before_trx_rollback_phase) { + /* No read-ahead to avoid thread deadlocks */ + return(0); + } + + if (ibuf_bitmap_page(zip_size, offset) + || trx_sys_hdr_page(space, offset)) { + + /* If it is an ibuf bitmap page or trx sys hdr, we do + no read-ahead, as that could break the ibuf page access + order */ + + return(0); + } + + /* Remember the tablespace version before we ask the tablespace size + below: if DISCARD + IMPORT changes the actual .ibd file meanwhile, we + do not try to read outside the bounds of the tablespace! */ + + tablespace_version = fil_space_get_version(space); + + buf_read_ahead_random_area = BUF_READ_AHEAD_RANDOM_AREA; + + low = (offset / buf_read_ahead_random_area) + * buf_read_ahead_random_area; + high = (offset / buf_read_ahead_random_area + 1) + * buf_read_ahead_random_area; + if (high > fil_space_get_size(space)) { + + high = fil_space_get_size(space); + } + + buf_pool_mutex_enter(); + + if (buf_pool->n_pend_reads + > buf_pool->curr_size / BUF_READ_AHEAD_PEND_LIMIT) { + buf_pool_mutex_exit(); + + return(0); + } + + /* Count how many blocks in the area have been recently accessed, + that is, reside near the start of the LRU list. */ + + for (i = low; i < high; i++) { + const buf_page_t* bpage = buf_page_hash_get(space, i); + + if (bpage + && buf_page_is_accessed(bpage) + && buf_page_peek_if_young(bpage)) { + + recent_blocks++; + + if (recent_blocks >= BUF_READ_AHEAD_RANDOM_THRESHOLD) { + + buf_pool_mutex_exit(); + goto read_ahead; + } + } + } + + buf_pool_mutex_exit(); + /* Do nothing */ + return(0); + +read_ahead: + /* Read all the suitable blocks within the area */ + + if (ibuf_inside()) { + ibuf_mode = BUF_READ_IBUF_PAGES_ONLY; + } else { + ibuf_mode = BUF_READ_ANY_PAGE; + } + + count = 0; + + for (i = low; i < high; i++) { + /* It is only sensible to do read-ahead in the non-sync aio + mode: hence FALSE as the first parameter */ + + if (!ibuf_bitmap_page(zip_size, i)) { + count += buf_read_page_low( + &err, FALSE, + ibuf_mode | OS_AIO_SIMULATED_WAKE_LATER, + space, zip_size, FALSE, + tablespace_version, i); + if (err == DB_TABLESPACE_DELETED) { + ut_print_timestamp(stderr); + fprintf(stderr, + " InnoDB: Warning: in random" + " readahead trying to access\n" + "InnoDB: tablespace %lu page %lu,\n" + "InnoDB: but the tablespace does not" + " exist or is just being dropped.\n", + (ulong) space, (ulong) i); + } + } + } + + /* In simulated aio we wake the aio handler threads only after + queuing all aio requests, in native aio the following call does + nothing: */ + + os_aio_simulated_wake_handler_threads(); + +#ifdef UNIV_DEBUG + if (buf_debug_prints && (count > 0)) { + fprintf(stderr, + "Random read-ahead space %lu offset %lu pages %lu\n", + (ulong) space, (ulong) offset, + (ulong) count); + } +#endif /* UNIV_DEBUG */ + + /* Read ahead is considered one I/O operation for the purpose of + LRU policy decision. */ + buf_LRU_stat_inc_io(); + + buf_pool->stat.n_ra_pages_read_rnd += count; + return(count); +} + + +/********************************************************************//** High-level function which reads a page asynchronously from a file to the buffer buf_pool if it is not already there. Sets the io_fix flag and sets an exclusive lock on the buffer frame. The flag is cleared and the x-lock @@ -175,6 +342,9 @@ buf_read_page( ulint count; ulint err; + count = buf_read_ahead_random(space, zip_size, offset); + srv_buf_pool_reads += count; + tablespace_version = fil_space_get_version(space); /* We do the i/o in the synchronous aio mode to save thread |