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Diffstat (limited to 'innobase/buf/buf0rea.c')
| -rw-r--r-- | innobase/buf/buf0rea.c | 559 |
1 files changed, 559 insertions, 0 deletions
diff --git a/innobase/buf/buf0rea.c b/innobase/buf/buf0rea.c new file mode 100644 index 00000000000..13e9ed0476b --- /dev/null +++ b/innobase/buf/buf0rea.c @@ -0,0 +1,559 @@ +/****************************************************** +The database buffer read + +(c) 1995 Innobase Oy + +Created 11/5/1995 Heikki Tuuri +*******************************************************/ + +#include "buf0rea.h" + +#include "fil0fil.h" +#include "mtr0mtr.h" + +#include "buf0buf.h" +#include "buf0flu.h" +#include "buf0lru.h" +#include "ibuf0ibuf.h" +#include "log0recv.h" +#include "trx0sys.h" +#include "os0file.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 + +/* The linear read-ahead threshold */ +#define BUF_READ_AHEAD_LINEAR_THRESHOLD (3 * BUF_READ_AHEAD_LINEAR_AREA / 8) + +/* If there are buf_pool->curr_size per the number below pending reads, then +read-ahead is not done: this is to prevent flooding the buffer pool with +i/o-fixed buffer blocks */ +#define BUF_READ_AHEAD_PEND_LIMIT 2 + +/************************************************************************ +Low-level function which reads a page asynchronously from a file to the +buffer buf_pool if it is not already there, in which case does nothing. +Sets the io_fix flag and sets an exclusive lock on the buffer frame. The +flag is cleared and the x-lock released by an i/o-handler thread. */ +static +ulint +buf_read_page_low( +/*==============*/ + /* out: 1 if a read request was queued, 0 if the page + already resided in buf_pool */ + ibool sync, /* in: TRUE if synchronous aio is desired */ + ulint mode, /* in: BUF_READ_IBUF_PAGES_ONLY, ..., + ORed to OS_AIO_SIMULATED_WAKE_LATER (see below + at read-ahead functions) */ + ulint space, /* in: space id */ + ulint offset) /* in: page number */ +{ + buf_block_t* block; + ulint wake_later; + + wake_later = mode & OS_AIO_SIMULATED_WAKE_LATER; + mode = mode & ~OS_AIO_SIMULATED_WAKE_LATER; + +#ifdef UNIV_LOG_DEBUG + if (space % 2 == 1) { + /* We are updating a replicate space while holding the + log mutex: the read must be handled before other reads + which might incur ibuf operations and thus write to the log */ + + printf("Log debug: reading replicate page in sync mode\n"); + + sync = TRUE; + } +#endif + if (trx_sys_hdr_page(space, offset)) { + + /* Trx sys header is so low in the latching order that we play + safe and do not leave the i/o-completion to an asynchronous + i/o-thread: */ + + sync = TRUE; + } + + block = buf_page_init_for_read(mode, space, offset); + + if (block != NULL) { + fil_io(OS_FILE_READ | wake_later, + sync, space, offset, 0, UNIV_PAGE_SIZE, + (void*)block->frame, (void*)block); + if (sync) { + /* The i/o is already completed when we arrive from + fil_read */ + buf_page_io_complete(block); + } + + return(1); + } + + return(0); +} + +/************************************************************************ +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. */ +static +ulint +buf_read_ahead_random( +/*==================*/ + /* out: 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 value > 0! */ + ulint space, /* in: space id */ + ulint offset) /* in: page number of a page which the current thread + wants to access */ +{ + buf_block_t* block; + ulint recent_blocks = 0; + ulint count; + ulint LRU_recent_limit; + ulint ibuf_mode; + ulint low, high; + ulint i; + + if (ibuf_bitmap_page(offset)) { + + /* If it is an ibuf bitmap page, we do no read-ahead, as + that could break the ibuf page access order */ + + return(0); + } + + 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); + } + + /* Get the minimum LRU_position field value for an initial segment + of the LRU list, to determine which blocks have recently been added + to the start of the list. */ + + LRU_recent_limit = buf_LRU_get_recent_limit(); + + mutex_enter(&(buf_pool->mutex)); + + if (buf_pool->n_pend_reads > + buf_pool->curr_size / BUF_READ_AHEAD_PEND_LIMIT) { + mutex_exit(&(buf_pool->mutex)); + + 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++) { + + block = buf_page_hash_get(space, i); + + if ((block) + && (block->LRU_position > LRU_recent_limit) + && block->accessed) { + + recent_blocks++; + } + } + + mutex_exit(&(buf_pool->mutex)); + + if (recent_blocks < BUF_READ_AHEAD_RANDOM_THRESHOLD) { + /* Do nothing */ + + return(0); + } + + /* 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(i)) { + + count += buf_read_page_low(FALSE, ibuf_mode + | OS_AIO_SIMULATED_WAKE_LATER, + space, 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(); + + if (buf_debug_prints && (count > 0)) { + + printf("Random read-ahead space %lu offset %lu pages %lu\n", + space, offset, 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 +released by the i/o-handler thread. Does a random read-ahead if it seems +sensible. */ + +ulint +buf_read_page( +/*==========*/ + /* out: number of page read requests issued: this can + be > 1 if read-ahead occurred */ + ulint space, /* in: space id */ + ulint offset) /* in: page number */ +{ + ulint count; + ulint count2; + + count = buf_read_ahead_random(space, offset); + + /* We do the i/o in the synchronous aio mode to save thread + switches: hence TRUE */ + + count2 = buf_read_page_low(TRUE, BUF_READ_ANY_PAGE, space, offset); + + /* Flush pages from the end of the LRU list if necessary */ + buf_flush_free_margin(); + + return(count + count2); +} + +/************************************************************************ +Applies linear read-ahead if in the buf_pool the page is a border page of +a linear read-ahead area and all the pages in the area have been accessed. +Does not read any page if the read-ahead mechanism is not activated. Note +that the the algorithm looks at the 'natural' adjacent successor and +predecessor of the page, which on the leaf level of a B-tree are the next +and previous page in the chain of leaves. To know these, the page specified +in (space, offset) must already be present in the buf_pool. Thus, the +natural way to use this function is to call it when a page in the buf_pool +is accessed the first time, calling this function just after it has been +bufferfixed. +NOTE 1: as this function looks at the natural predecessor and successor +fields on the page, what happens, if these are not initialized to any +sensible value? No problem, before applying read-ahead we check that the +area to read is within the span of the space, if not, read-ahead is not +applied. An uninitialized value may result in a useless read operation, but +only very improbably. +NOTE 2: 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 3: 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 io. */ + +ulint +buf_read_ahead_linear( +/*==================*/ + /* out: number of page read requests issued */ + ulint space, /* in: space id */ + ulint offset) /* in: page number of a page; NOTE: the current thread + must want access to this page (see NOTE 3 above) */ +{ + buf_block_t* block; + buf_frame_t* frame; + buf_block_t* pred_block = NULL; + ulint pred_offset; + ulint succ_offset; + ulint count; + int asc_or_desc; + ulint new_offset; + ulint fail_count; + ulint ibuf_mode; + ulint low, high; + ulint i; + + if (ibuf_bitmap_page(offset)) { + /* If it is an ibuf bitmap page, we do no read-ahead, as + that could break the ibuf page access order */ + + return(0); + } + + low = (offset / BUF_READ_AHEAD_LINEAR_AREA) + * BUF_READ_AHEAD_LINEAR_AREA; + high = (offset / BUF_READ_AHEAD_LINEAR_AREA + 1) + * BUF_READ_AHEAD_LINEAR_AREA; + + if ((offset != low) && (offset != high - 1)) { + /* This is not a border page of the area: return */ + + return(0); + } + + if (high > fil_space_get_size(space)) { + /* The area is not whole, return */ + + return(0); + } + + mutex_enter(&(buf_pool->mutex)); + + if (buf_pool->n_pend_reads > + buf_pool->curr_size / BUF_READ_AHEAD_PEND_LIMIT) { + mutex_exit(&(buf_pool->mutex)); + + return(0); + } + + /* Check that almost all pages in the area have been accessed; if + offset == low, the accesses must be in a descending order, otherwise, + in an ascending order. */ + + asc_or_desc = 1; + + if (offset == low) { + asc_or_desc = -1; + } + + fail_count = 0; + + for (i = low; i < high; i++) { + + block = buf_page_hash_get(space, i); + + if ((block == NULL) || !block->accessed) { + + /* Not accessed */ + fail_count++; + + } else if (pred_block && (ut_ulint_cmp(block->LRU_position, + pred_block->LRU_position) + != asc_or_desc)) { + + /* Accesses not in the right order */ + + fail_count++; + pred_block = block; + } + } + + if (fail_count > BUF_READ_AHEAD_LINEAR_AREA - + BUF_READ_AHEAD_LINEAR_THRESHOLD) { + /* Too many failures: return */ + + mutex_exit(&(buf_pool->mutex)); + + return(0); + } + + /* If we got this far, we know that enough pages in the area have + been accessed in the right order: linear read-ahead can be sensible */ + + block = buf_page_hash_get(space, offset); + + if (block == NULL) { + mutex_exit(&(buf_pool->mutex)); + + return(0); + } + + frame = block->frame; + + /* Read the natural predecessor and successor page addresses from + the page; NOTE that because the calling thread may have an x-latch + on the page, we do not acquire an s-latch on the page, this is to + prevent deadlocks. Even if we read values which are nonsense, the + algorithm will work. */ + + pred_offset = fil_page_get_prev(frame); + succ_offset = fil_page_get_next(frame); + + mutex_exit(&(buf_pool->mutex)); + + if ((offset == low) && (succ_offset == offset + 1)) { + + /* This is ok, we can continue */ + new_offset = pred_offset; + + } else if ((offset == high - 1) && (pred_offset == offset - 1)) { + + /* This is ok, we can continue */ + new_offset = succ_offset; + } else { + /* Successor or predecessor not in the right order */ + + return(0); + } + + low = (new_offset / BUF_READ_AHEAD_LINEAR_AREA) + * BUF_READ_AHEAD_LINEAR_AREA; + high = (new_offset / BUF_READ_AHEAD_LINEAR_AREA + 1) + * BUF_READ_AHEAD_LINEAR_AREA; + + if ((new_offset != low) && (new_offset != high - 1)) { + /* This is not a border page of the area: return */ + + return(0); + } + + if (high > fil_space_get_size(space)) { + /* The area is not whole, return */ + + return(0); + } + + /* If we got this far, read-ahead can be sensible: do it */ + + 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(i)) { + count += buf_read_page_low(FALSE, ibuf_mode + | OS_AIO_SIMULATED_WAKE_LATER, + space, 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(); + + /* Flush pages from the end of the LRU list if necessary */ + buf_flush_free_margin(); + + if (buf_debug_prints && (count > 0)) { + printf( + "LINEAR read-ahead space %lu offset %lu pages %lu\n", + space, offset, count); + } + + return(count); +} + +/************************************************************************ +Issues read requests for pages which the ibuf module wants to read in, in +order to contract insert buffer trees. Technically, this function is like +a read-ahead function. */ + +void +buf_read_ibuf_merge_pages( +/*======================*/ + ibool sync, /* in: TRUE if the caller wants this function + to wait for the highest address page to get + read in, before this function returns */ + ulint space, /* in: space id */ + ulint* page_nos, /* in: array of page numbers to read, with the + highest page number the last in the array */ + ulint n_stored) /* in: number of page numbers in the array */ +{ + ulint i; + + ut_ad(!ibuf_inside()); +#ifdef UNIV_IBUF_DEBUG + ut_a(n_stored < UNIV_PAGE_SIZE); +#endif + while (buf_pool->n_pend_reads > + buf_pool->curr_size / BUF_READ_AHEAD_PEND_LIMIT) { + os_thread_sleep(500000); + } + + for (i = 0; i < n_stored; i++) { + if ((i + 1 == n_stored) && sync) { + buf_read_page_low(TRUE, BUF_READ_ANY_PAGE, space, + page_nos[i]); + } else { + buf_read_page_low(FALSE, BUF_READ_ANY_PAGE, space, + page_nos[i]); + } + } + + /* Flush pages from the end of the LRU list if necessary */ + buf_flush_free_margin(); + + if (buf_debug_prints) { + printf("Ibuf merge read-ahead space %lu pages %lu\n", + space, n_stored); + } +} + +/************************************************************************ +Issues read requests for pages which recovery wants to read in. */ + +void +buf_read_recv_pages( +/*================*/ + ibool sync, /* in: TRUE if the caller wants this function + to wait for the highest address page to get + read in, before this function returns */ + ulint space, /* in: space id */ + ulint* page_nos, /* in: array of page numbers to read, with the + highest page number the last in the array */ + ulint n_stored) /* in: number of page numbers in the array */ +{ + ulint i; + + for (i = 0; i < n_stored; i++) { + + while (buf_pool->n_pend_reads >= RECV_POOL_N_FREE_BLOCKS / 2) { + + os_aio_simulated_wake_handler_threads(); + os_thread_sleep(500000); + } + + if ((i + 1 == n_stored) && sync) { + buf_read_page_low(TRUE, BUF_READ_ANY_PAGE, space, + page_nos[i]); + } else { + buf_read_page_low(FALSE, BUF_READ_ANY_PAGE + | OS_AIO_SIMULATED_WAKE_LATER, + space, page_nos[i]); + } + } + + os_aio_simulated_wake_handler_threads(); + + /* Flush pages from the end of the LRU list if necessary */ + buf_flush_free_margin(); + + if (buf_debug_prints) { + printf("Recovery applies read-ahead pages %lu\n", n_stored); + } +} |