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Diffstat (limited to 'src/backend/access/transam/slru.c')
| -rw-r--r-- | src/backend/access/transam/slru.c | 1615 |
1 files changed, 1615 insertions, 0 deletions
diff --git a/src/backend/access/transam/slru.c b/src/backend/access/transam/slru.c new file mode 100644 index 0000000..af57fe9 --- /dev/null +++ b/src/backend/access/transam/slru.c @@ -0,0 +1,1615 @@ +/*------------------------------------------------------------------------- + * + * slru.c + * Simple LRU buffering for transaction status logfiles + * + * We use a simple least-recently-used scheme to manage a pool of page + * buffers. Under ordinary circumstances we expect that write + * traffic will occur mostly to the latest page (and to the just-prior + * page, soon after a page transition). Read traffic will probably touch + * a larger span of pages, but in any case a fairly small number of page + * buffers should be sufficient. So, we just search the buffers using plain + * linear search; there's no need for a hashtable or anything fancy. + * The management algorithm is straight LRU except that we will never swap + * out the latest page (since we know it's going to be hit again eventually). + * + * We use a control LWLock to protect the shared data structures, plus + * per-buffer LWLocks that synchronize I/O for each buffer. The control lock + * must be held to examine or modify any shared state. A process that is + * reading in or writing out a page buffer does not hold the control lock, + * only the per-buffer lock for the buffer it is working on. + * + * "Holding the control lock" means exclusive lock in all cases except for + * SimpleLruReadPage_ReadOnly(); see comments for SlruRecentlyUsed() for + * the implications of that. + * + * When initiating I/O on a buffer, we acquire the per-buffer lock exclusively + * before releasing the control lock. The per-buffer lock is released after + * completing the I/O, re-acquiring the control lock, and updating the shared + * state. (Deadlock is not possible here, because we never try to initiate + * I/O when someone else is already doing I/O on the same buffer.) + * To wait for I/O to complete, release the control lock, acquire the + * per-buffer lock in shared mode, immediately release the per-buffer lock, + * reacquire the control lock, and then recheck state (since arbitrary things + * could have happened while we didn't have the lock). + * + * As with the regular buffer manager, it is possible for another process + * to re-dirty a page that is currently being written out. This is handled + * by re-setting the page's page_dirty flag. + * + * + * Portions Copyright (c) 1996-2022, PostgreSQL Global Development Group + * Portions Copyright (c) 1994, Regents of the University of California + * + * src/backend/access/transam/slru.c + * + *------------------------------------------------------------------------- + */ +#include "postgres.h" + +#include <fcntl.h> +#include <sys/stat.h> +#include <unistd.h> + +#include "access/slru.h" +#include "access/transam.h" +#include "access/xlog.h" +#include "access/xlogutils.h" +#include "miscadmin.h" +#include "pgstat.h" +#include "storage/fd.h" +#include "storage/shmem.h" + +#define SlruFileName(ctl, path, seg) \ + snprintf(path, MAXPGPATH, "%s/%04X", (ctl)->Dir, seg) + +/* + * During SimpleLruWriteAll(), we will usually not need to write more than one + * or two physical files, but we may need to write several pages per file. We + * can consolidate the I/O requests by leaving files open until control returns + * to SimpleLruWriteAll(). This data structure remembers which files are open. + */ +#define MAX_WRITEALL_BUFFERS 16 + +typedef struct SlruWriteAllData +{ + int num_files; /* # files actually open */ + int fd[MAX_WRITEALL_BUFFERS]; /* their FD's */ + int segno[MAX_WRITEALL_BUFFERS]; /* their log seg#s */ +} SlruWriteAllData; + +typedef struct SlruWriteAllData *SlruWriteAll; + +/* + * Populate a file tag describing a segment file. We only use the segment + * number, since we can derive everything else we need by having separate + * sync handler functions for clog, multixact etc. + */ +#define INIT_SLRUFILETAG(a,xx_handler,xx_segno) \ +( \ + memset(&(a), 0, sizeof(FileTag)), \ + (a).handler = (xx_handler), \ + (a).segno = (xx_segno) \ +) + +/* + * Macro to mark a buffer slot "most recently used". Note multiple evaluation + * of arguments! + * + * The reason for the if-test is that there are often many consecutive + * accesses to the same page (particularly the latest page). By suppressing + * useless increments of cur_lru_count, we reduce the probability that old + * pages' counts will "wrap around" and make them appear recently used. + * + * We allow this code to be executed concurrently by multiple processes within + * SimpleLruReadPage_ReadOnly(). As long as int reads and writes are atomic, + * this should not cause any completely-bogus values to enter the computation. + * However, it is possible for either cur_lru_count or individual + * page_lru_count entries to be "reset" to lower values than they should have, + * in case a process is delayed while it executes this macro. With care in + * SlruSelectLRUPage(), this does little harm, and in any case the absolute + * worst possible consequence is a nonoptimal choice of page to evict. The + * gain from allowing concurrent reads of SLRU pages seems worth it. + */ +#define SlruRecentlyUsed(shared, slotno) \ + do { \ + int new_lru_count = (shared)->cur_lru_count; \ + if (new_lru_count != (shared)->page_lru_count[slotno]) { \ + (shared)->cur_lru_count = ++new_lru_count; \ + (shared)->page_lru_count[slotno] = new_lru_count; \ + } \ + } while (0) + +/* Saved info for SlruReportIOError */ +typedef enum +{ + SLRU_OPEN_FAILED, + SLRU_SEEK_FAILED, + SLRU_READ_FAILED, + SLRU_WRITE_FAILED, + SLRU_FSYNC_FAILED, + SLRU_CLOSE_FAILED +} SlruErrorCause; + +static SlruErrorCause slru_errcause; +static int slru_errno; + + +static void SimpleLruZeroLSNs(SlruCtl ctl, int slotno); +static void SimpleLruWaitIO(SlruCtl ctl, int slotno); +static void SlruInternalWritePage(SlruCtl ctl, int slotno, SlruWriteAll fdata); +static bool SlruPhysicalReadPage(SlruCtl ctl, int pageno, int slotno); +static bool SlruPhysicalWritePage(SlruCtl ctl, int pageno, int slotno, + SlruWriteAll fdata); +static void SlruReportIOError(SlruCtl ctl, int pageno, TransactionId xid); +static int SlruSelectLRUPage(SlruCtl ctl, int pageno); + +static bool SlruScanDirCbDeleteCutoff(SlruCtl ctl, char *filename, + int segpage, void *data); +static void SlruInternalDeleteSegment(SlruCtl ctl, int segno); + +/* + * Initialization of shared memory + */ + +Size +SimpleLruShmemSize(int nslots, int nlsns) +{ + Size sz; + + /* we assume nslots isn't so large as to risk overflow */ + sz = MAXALIGN(sizeof(SlruSharedData)); + sz += MAXALIGN(nslots * sizeof(char *)); /* page_buffer[] */ + sz += MAXALIGN(nslots * sizeof(SlruPageStatus)); /* page_status[] */ + sz += MAXALIGN(nslots * sizeof(bool)); /* page_dirty[] */ + sz += MAXALIGN(nslots * sizeof(int)); /* page_number[] */ + sz += MAXALIGN(nslots * sizeof(int)); /* page_lru_count[] */ + sz += MAXALIGN(nslots * sizeof(LWLockPadded)); /* buffer_locks[] */ + + if (nlsns > 0) + sz += MAXALIGN(nslots * nlsns * sizeof(XLogRecPtr)); /* group_lsn[] */ + + return BUFFERALIGN(sz) + BLCKSZ * nslots; +} + +/* + * Initialize, or attach to, a simple LRU cache in shared memory. + * + * ctl: address of local (unshared) control structure. + * name: name of SLRU. (This is user-visible, pick with care!) + * nslots: number of page slots to use. + * nlsns: number of LSN groups per page (set to zero if not relevant). + * ctllock: LWLock to use to control access to the shared control structure. + * subdir: PGDATA-relative subdirectory that will contain the files. + * tranche_id: LWLock tranche ID to use for the SLRU's per-buffer LWLocks. + * sync_handler: which set of functions to use to handle sync requests + */ +void +SimpleLruInit(SlruCtl ctl, const char *name, int nslots, int nlsns, + LWLock *ctllock, const char *subdir, int tranche_id, + SyncRequestHandler sync_handler) +{ + SlruShared shared; + bool found; + + shared = (SlruShared) ShmemInitStruct(name, + SimpleLruShmemSize(nslots, nlsns), + &found); + + if (!IsUnderPostmaster) + { + /* Initialize locks and shared memory area */ + char *ptr; + Size offset; + int slotno; + + Assert(!found); + + memset(shared, 0, sizeof(SlruSharedData)); + + shared->ControlLock = ctllock; + + shared->num_slots = nslots; + shared->lsn_groups_per_page = nlsns; + + shared->cur_lru_count = 0; + + /* shared->latest_page_number will be set later */ + + shared->slru_stats_idx = pgstat_get_slru_index(name); + + ptr = (char *) shared; + offset = MAXALIGN(sizeof(SlruSharedData)); + shared->page_buffer = (char **) (ptr + offset); + offset += MAXALIGN(nslots * sizeof(char *)); + shared->page_status = (SlruPageStatus *) (ptr + offset); + offset += MAXALIGN(nslots * sizeof(SlruPageStatus)); + shared->page_dirty = (bool *) (ptr + offset); + offset += MAXALIGN(nslots * sizeof(bool)); + shared->page_number = (int *) (ptr + offset); + offset += MAXALIGN(nslots * sizeof(int)); + shared->page_lru_count = (int *) (ptr + offset); + offset += MAXALIGN(nslots * sizeof(int)); + + /* Initialize LWLocks */ + shared->buffer_locks = (LWLockPadded *) (ptr + offset); + offset += MAXALIGN(nslots * sizeof(LWLockPadded)); + + if (nlsns > 0) + { + shared->group_lsn = (XLogRecPtr *) (ptr + offset); + offset += MAXALIGN(nslots * nlsns * sizeof(XLogRecPtr)); + } + + ptr += BUFFERALIGN(offset); + for (slotno = 0; slotno < nslots; slotno++) + { + LWLockInitialize(&shared->buffer_locks[slotno].lock, + tranche_id); + + shared->page_buffer[slotno] = ptr; + shared->page_status[slotno] = SLRU_PAGE_EMPTY; + shared->page_dirty[slotno] = false; + shared->page_lru_count[slotno] = 0; + ptr += BLCKSZ; + } + + /* Should fit to estimated shmem size */ + Assert(ptr - (char *) shared <= SimpleLruShmemSize(nslots, nlsns)); + } + else + Assert(found); + + /* + * Initialize the unshared control struct, including directory path. We + * assume caller set PagePrecedes. + */ + ctl->shared = shared; + ctl->sync_handler = sync_handler; + strlcpy(ctl->Dir, subdir, sizeof(ctl->Dir)); +} + +/* + * Initialize (or reinitialize) a page to zeroes. + * + * The page is not actually written, just set up in shared memory. + * The slot number of the new page is returned. + * + * Control lock must be held at entry, and will be held at exit. + */ +int +SimpleLruZeroPage(SlruCtl ctl, int pageno) +{ + SlruShared shared = ctl->shared; + int slotno; + + /* Find a suitable buffer slot for the page */ + slotno = SlruSelectLRUPage(ctl, pageno); + Assert(shared->page_status[slotno] == SLRU_PAGE_EMPTY || + (shared->page_status[slotno] == SLRU_PAGE_VALID && + !shared->page_dirty[slotno]) || + shared->page_number[slotno] == pageno); + + /* Mark the slot as containing this page */ + shared->page_number[slotno] = pageno; + shared->page_status[slotno] = SLRU_PAGE_VALID; + shared->page_dirty[slotno] = true; + SlruRecentlyUsed(shared, slotno); + + /* Set the buffer to zeroes */ + MemSet(shared->page_buffer[slotno], 0, BLCKSZ); + + /* Set the LSNs for this new page to zero */ + SimpleLruZeroLSNs(ctl, slotno); + + /* Assume this page is now the latest active page */ + shared->latest_page_number = pageno; + + /* update the stats counter of zeroed pages */ + pgstat_count_slru_page_zeroed(shared->slru_stats_idx); + + return slotno; +} + +/* + * Zero all the LSNs we store for this slru page. + * + * This should be called each time we create a new page, and each time we read + * in a page from disk into an existing buffer. (Such an old page cannot + * have any interesting LSNs, since we'd have flushed them before writing + * the page in the first place.) + * + * This assumes that InvalidXLogRecPtr is bitwise-all-0. + */ +static void +SimpleLruZeroLSNs(SlruCtl ctl, int slotno) +{ + SlruShared shared = ctl->shared; + + if (shared->lsn_groups_per_page > 0) + MemSet(&shared->group_lsn[slotno * shared->lsn_groups_per_page], 0, + shared->lsn_groups_per_page * sizeof(XLogRecPtr)); +} + +/* + * Wait for any active I/O on a page slot to finish. (This does not + * guarantee that new I/O hasn't been started before we return, though. + * In fact the slot might not even contain the same page anymore.) + * + * Control lock must be held at entry, and will be held at exit. + */ +static void +SimpleLruWaitIO(SlruCtl ctl, int slotno) +{ + SlruShared shared = ctl->shared; + + /* See notes at top of file */ + LWLockRelease(shared->ControlLock); + LWLockAcquire(&shared->buffer_locks[slotno].lock, LW_SHARED); + LWLockRelease(&shared->buffer_locks[slotno].lock); + LWLockAcquire(shared->ControlLock, LW_EXCLUSIVE); + + /* + * If the slot is still in an io-in-progress state, then either someone + * already started a new I/O on the slot, or a previous I/O failed and + * neglected to reset the page state. That shouldn't happen, really, but + * it seems worth a few extra cycles to check and recover from it. We can + * cheaply test for failure by seeing if the buffer lock is still held (we + * assume that transaction abort would release the lock). + */ + if (shared->page_status[slotno] == SLRU_PAGE_READ_IN_PROGRESS || + shared->page_status[slotno] == SLRU_PAGE_WRITE_IN_PROGRESS) + { + if (LWLockConditionalAcquire(&shared->buffer_locks[slotno].lock, LW_SHARED)) + { + /* indeed, the I/O must have failed */ + if (shared->page_status[slotno] == SLRU_PAGE_READ_IN_PROGRESS) + shared->page_status[slotno] = SLRU_PAGE_EMPTY; + else /* write_in_progress */ + { + shared->page_status[slotno] = SLRU_PAGE_VALID; + shared->page_dirty[slotno] = true; + } + LWLockRelease(&shared->buffer_locks[slotno].lock); + } + } +} + +/* + * Find a page in a shared buffer, reading it in if necessary. + * The page number must correspond to an already-initialized page. + * + * If write_ok is true then it is OK to return a page that is in + * WRITE_IN_PROGRESS state; it is the caller's responsibility to be sure + * that modification of the page is safe. If write_ok is false then we + * will not return the page until it is not undergoing active I/O. + * + * The passed-in xid is used only for error reporting, and may be + * InvalidTransactionId if no specific xid is associated with the action. + * + * Return value is the shared-buffer slot number now holding the page. + * The buffer's LRU access info is updated. + * + * Control lock must be held at entry, and will be held at exit. + */ +int +SimpleLruReadPage(SlruCtl ctl, int pageno, bool write_ok, + TransactionId xid) +{ + SlruShared shared = ctl->shared; + + /* Outer loop handles restart if we must wait for someone else's I/O */ + for (;;) + { + int slotno; + bool ok; + + /* See if page already is in memory; if not, pick victim slot */ + slotno = SlruSelectLRUPage(ctl, pageno); + + /* Did we find the page in memory? */ + if (shared->page_number[slotno] == pageno && + shared->page_status[slotno] != SLRU_PAGE_EMPTY) + { + /* + * If page is still being read in, we must wait for I/O. Likewise + * if the page is being written and the caller said that's not OK. + */ + if (shared->page_status[slotno] == SLRU_PAGE_READ_IN_PROGRESS || + (shared->page_status[slotno] == SLRU_PAGE_WRITE_IN_PROGRESS && + !write_ok)) + { + SimpleLruWaitIO(ctl, slotno); + /* Now we must recheck state from the top */ + continue; + } + /* Otherwise, it's ready to use */ + SlruRecentlyUsed(shared, slotno); + + /* update the stats counter of pages found in the SLRU */ + pgstat_count_slru_page_hit(shared->slru_stats_idx); + + return slotno; + } + + /* We found no match; assert we selected a freeable slot */ + Assert(shared->page_status[slotno] == SLRU_PAGE_EMPTY || + (shared->page_status[slotno] == SLRU_PAGE_VALID && + !shared->page_dirty[slotno])); + + /* Mark the slot read-busy */ + shared->page_number[slotno] = pageno; + shared->page_status[slotno] = SLRU_PAGE_READ_IN_PROGRESS; + shared->page_dirty[slotno] = false; + + /* Acquire per-buffer lock (cannot deadlock, see notes at top) */ + LWLockAcquire(&shared->buffer_locks[slotno].lock, LW_EXCLUSIVE); + + /* Release control lock while doing I/O */ + LWLockRelease(shared->ControlLock); + + /* Do the read */ + ok = SlruPhysicalReadPage(ctl, pageno, slotno); + + /* Set the LSNs for this newly read-in page to zero */ + SimpleLruZeroLSNs(ctl, slotno); + + /* Re-acquire control lock and update page state */ + LWLockAcquire(shared->ControlLock, LW_EXCLUSIVE); + + Assert(shared->page_number[slotno] == pageno && + shared->page_status[slotno] == SLRU_PAGE_READ_IN_PROGRESS && + !shared->page_dirty[slotno]); + + shared->page_status[slotno] = ok ? SLRU_PAGE_VALID : SLRU_PAGE_EMPTY; + + LWLockRelease(&shared->buffer_locks[slotno].lock); + + /* Now it's okay to ereport if we failed */ + if (!ok) + SlruReportIOError(ctl, pageno, xid); + + SlruRecentlyUsed(shared, slotno); + + /* update the stats counter of pages not found in SLRU */ + pgstat_count_slru_page_read(shared->slru_stats_idx); + + return slotno; + } +} + +/* + * Find a page in a shared buffer, reading it in if necessary. + * The page number must correspond to an already-initialized page. + * The caller must intend only read-only access to the page. + * + * The passed-in xid is used only for error reporting, and may be + * InvalidTransactionId if no specific xid is associated with the action. + * + * Return value is the shared-buffer slot number now holding the page. + * The buffer's LRU access info is updated. + * + * Control lock must NOT be held at entry, but will be held at exit. + * It is unspecified whether the lock will be shared or exclusive. + */ +int +SimpleLruReadPage_ReadOnly(SlruCtl ctl, int pageno, TransactionId xid) +{ + SlruShared shared = ctl->shared; + int slotno; + + /* Try to find the page while holding only shared lock */ + LWLockAcquire(shared->ControlLock, LW_SHARED); + + /* See if page is already in a buffer */ + for (slotno = 0; slotno < shared->num_slots; slotno++) + { + if (shared->page_number[slotno] == pageno && + shared->page_status[slotno] != SLRU_PAGE_EMPTY && + shared->page_status[slotno] != SLRU_PAGE_READ_IN_PROGRESS) + { + /* See comments for SlruRecentlyUsed macro */ + SlruRecentlyUsed(shared, slotno); + + /* update the stats counter of pages found in the SLRU */ + pgstat_count_slru_page_hit(shared->slru_stats_idx); + + return slotno; + } + } + + /* No luck, so switch to normal exclusive lock and do regular read */ + LWLockRelease(shared->ControlLock); + LWLockAcquire(shared->ControlLock, LW_EXCLUSIVE); + + return SimpleLruReadPage(ctl, pageno, true, xid); +} + +/* + * Write a page from a shared buffer, if necessary. + * Does nothing if the specified slot is not dirty. + * + * NOTE: only one write attempt is made here. Hence, it is possible that + * the page is still dirty at exit (if someone else re-dirtied it during + * the write). However, we *do* attempt a fresh write even if the page + * is already being written; this is for checkpoints. + * + * Control lock must be held at entry, and will be held at exit. + */ +static void +SlruInternalWritePage(SlruCtl ctl, int slotno, SlruWriteAll fdata) +{ + SlruShared shared = ctl->shared; + int pageno = shared->page_number[slotno]; + bool ok; + + /* If a write is in progress, wait for it to finish */ + while (shared->page_status[slotno] == SLRU_PAGE_WRITE_IN_PROGRESS && + shared->page_number[slotno] == pageno) + { + SimpleLruWaitIO(ctl, slotno); + } + + /* + * Do nothing if page is not dirty, or if buffer no longer contains the + * same page we were called for. + */ + if (!shared->page_dirty[slotno] || + shared->page_status[slotno] != SLRU_PAGE_VALID || + shared->page_number[slotno] != pageno) + return; + + /* + * Mark the slot write-busy, and clear the dirtybit. After this point, a + * transaction status update on this page will mark it dirty again. + */ + shared->page_status[slotno] = SLRU_PAGE_WRITE_IN_PROGRESS; + shared->page_dirty[slotno] = false; + + /* Acquire per-buffer lock (cannot deadlock, see notes at top) */ + LWLockAcquire(&shared->buffer_locks[slotno].lock, LW_EXCLUSIVE); + + /* Release control lock while doing I/O */ + LWLockRelease(shared->ControlLock); + + /* Do the write */ + ok = SlruPhysicalWritePage(ctl, pageno, slotno, fdata); + + /* If we failed, and we're in a flush, better close the files */ + if (!ok && fdata) + { + int i; + + for (i = 0; i < fdata->num_files; i++) + CloseTransientFile(fdata->fd[i]); + } + + /* Re-acquire control lock and update page state */ + LWLockAcquire(shared->ControlLock, LW_EXCLUSIVE); + + Assert(shared->page_number[slotno] == pageno && + shared->page_status[slotno] == SLRU_PAGE_WRITE_IN_PROGRESS); + + /* If we failed to write, mark the page dirty again */ + if (!ok) + shared->page_dirty[slotno] = true; + + shared->page_status[slotno] = SLRU_PAGE_VALID; + + LWLockRelease(&shared->buffer_locks[slotno].lock); + + /* Now it's okay to ereport if we failed */ + if (!ok) + SlruReportIOError(ctl, pageno, InvalidTransactionId); + + /* If part of a checkpoint, count this as a buffer written. */ + if (fdata) + CheckpointStats.ckpt_bufs_written++; +} + +/* + * Wrapper of SlruInternalWritePage, for external callers. + * fdata is always passed a NULL here. + */ +void +SimpleLruWritePage(SlruCtl ctl, int slotno) +{ + SlruInternalWritePage(ctl, slotno, NULL); +} + +/* + * Return whether the given page exists on disk. + * + * A false return means that either the file does not exist, or that it's not + * large enough to contain the given page. + */ +bool +SimpleLruDoesPhysicalPageExist(SlruCtl ctl, int pageno) +{ + int segno = pageno / SLRU_PAGES_PER_SEGMENT; + int rpageno = pageno % SLRU_PAGES_PER_SEGMENT; + int offset = rpageno * BLCKSZ; + char path[MAXPGPATH]; + int fd; + bool result; + off_t endpos; + + /* update the stats counter of checked pages */ + pgstat_count_slru_page_exists(ctl->shared->slru_stats_idx); + + SlruFileName(ctl, path, segno); + + fd = OpenTransientFile(path, O_RDONLY | PG_BINARY); + if (fd < 0) + { + /* expected: file doesn't exist */ + if (errno == ENOENT) + return false; + + /* report error normally */ + slru_errcause = SLRU_OPEN_FAILED; + slru_errno = errno; + SlruReportIOError(ctl, pageno, 0); + } + + if ((endpos = lseek(fd, 0, SEEK_END)) < 0) + { + slru_errcause = SLRU_SEEK_FAILED; + slru_errno = errno; + SlruReportIOError(ctl, pageno, 0); + } + + result = endpos >= (off_t) (offset + BLCKSZ); + + if (CloseTransientFile(fd) != 0) + { + slru_errcause = SLRU_CLOSE_FAILED; + slru_errno = errno; + return false; + } + + return result; +} + +/* + * Physical read of a (previously existing) page into a buffer slot + * + * On failure, we cannot just ereport(ERROR) since caller has put state in + * shared memory that must be undone. So, we return false and save enough + * info in static variables to let SlruReportIOError make the report. + * + * For now, assume it's not worth keeping a file pointer open across + * read/write operations. We could cache one virtual file pointer ... + */ +static bool +SlruPhysicalReadPage(SlruCtl ctl, int pageno, int slotno) +{ + SlruShared shared = ctl->shared; + int segno = pageno / SLRU_PAGES_PER_SEGMENT; + int rpageno = pageno % SLRU_PAGES_PER_SEGMENT; + off_t offset = rpageno * BLCKSZ; + char path[MAXPGPATH]; + int fd; + + SlruFileName(ctl, path, segno); + + /* + * In a crash-and-restart situation, it's possible for us to receive + * commands to set the commit status of transactions whose bits are in + * already-truncated segments of the commit log (see notes in + * SlruPhysicalWritePage). Hence, if we are InRecovery, allow the case + * where the file doesn't exist, and return zeroes instead. + */ + fd = OpenTransientFile(path, O_RDONLY | PG_BINARY); + if (fd < 0) + { + if (errno != ENOENT || !InRecovery) + { + slru_errcause = SLRU_OPEN_FAILED; + slru_errno = errno; + return false; + } + + ereport(LOG, + (errmsg("file \"%s\" doesn't exist, reading as zeroes", + path))); + MemSet(shared->page_buffer[slotno], 0, BLCKSZ); + return true; + } + + errno = 0; + pgstat_report_wait_start(WAIT_EVENT_SLRU_READ); + if (pg_pread(fd, shared->page_buffer[slotno], BLCKSZ, offset) != BLCKSZ) + { + pgstat_report_wait_end(); + slru_errcause = SLRU_READ_FAILED; + slru_errno = errno; + CloseTransientFile(fd); + return false; + } + pgstat_report_wait_end(); + + if (CloseTransientFile(fd) != 0) + { + slru_errcause = SLRU_CLOSE_FAILED; + slru_errno = errno; + return false; + } + + return true; +} + +/* + * Physical write of a page from a buffer slot + * + * On failure, we cannot just ereport(ERROR) since caller has put state in + * shared memory that must be undone. So, we return false and save enough + * info in static variables to let SlruReportIOError make the report. + * + * For now, assume it's not worth keeping a file pointer open across + * independent read/write operations. We do batch operations during + * SimpleLruWriteAll, though. + * + * fdata is NULL for a standalone write, pointer to open-file info during + * SimpleLruWriteAll. + */ +static bool +SlruPhysicalWritePage(SlruCtl ctl, int pageno, int slotno, SlruWriteAll fdata) +{ + SlruShared shared = ctl->shared; + int segno = pageno / SLRU_PAGES_PER_SEGMENT; + int rpageno = pageno % SLRU_PAGES_PER_SEGMENT; + off_t offset = rpageno * BLCKSZ; + char path[MAXPGPATH]; + int fd = -1; + + /* update the stats counter of written pages */ + pgstat_count_slru_page_written(shared->slru_stats_idx); + + /* + * Honor the write-WAL-before-data rule, if appropriate, so that we do not + * write out data before associated WAL records. This is the same action + * performed during FlushBuffer() in the main buffer manager. + */ + if (shared->group_lsn != NULL) + { + /* + * We must determine the largest async-commit LSN for the page. This + * is a bit tedious, but since this entire function is a slow path + * anyway, it seems better to do this here than to maintain a per-page + * LSN variable (which'd need an extra comparison in the + * transaction-commit path). + */ + XLogRecPtr max_lsn; + int lsnindex, + lsnoff; + + lsnindex = slotno * shared->lsn_groups_per_page; + max_lsn = shared->group_lsn[lsnindex++]; + for (lsnoff = 1; lsnoff < shared->lsn_groups_per_page; lsnoff++) + { + XLogRecPtr this_lsn = shared->group_lsn[lsnindex++]; + + if (max_lsn < this_lsn) + max_lsn = this_lsn; + } + + if (!XLogRecPtrIsInvalid(max_lsn)) + { + /* + * As noted above, elog(ERROR) is not acceptable here, so if + * XLogFlush were to fail, we must PANIC. This isn't much of a + * restriction because XLogFlush is just about all critical + * section anyway, but let's make sure. + */ + START_CRIT_SECTION(); + XLogFlush(max_lsn); + END_CRIT_SECTION(); + } + } + + /* + * During a WriteAll, we may already have the desired file open. + */ + if (fdata) + { + int i; + + for (i = 0; i < fdata->num_files; i++) + { + if (fdata->segno[i] == segno) + { + fd = fdata->fd[i]; + break; + } + } + } + + if (fd < 0) + { + /* + * If the file doesn't already exist, we should create it. It is + * possible for this to need to happen when writing a page that's not + * first in its segment; we assume the OS can cope with that. (Note: + * it might seem that it'd be okay to create files only when + * SimpleLruZeroPage is called for the first page of a segment. + * However, if after a crash and restart the REDO logic elects to + * replay the log from a checkpoint before the latest one, then it's + * possible that we will get commands to set transaction status of + * transactions that have already been truncated from the commit log. + * Easiest way to deal with that is to accept references to + * nonexistent files here and in SlruPhysicalReadPage.) + * + * Note: it is possible for more than one backend to be executing this + * code simultaneously for different pages of the same file. Hence, + * don't use O_EXCL or O_TRUNC or anything like that. + */ + SlruFileName(ctl, path, segno); + fd = OpenTransientFile(path, O_RDWR | O_CREAT | PG_BINARY); + if (fd < 0) + { + slru_errcause = SLRU_OPEN_FAILED; + slru_errno = errno; + return false; + } + + if (fdata) + { + if (fdata->num_files < MAX_WRITEALL_BUFFERS) + { + fdata->fd[fdata->num_files] = fd; + fdata->segno[fdata->num_files] = segno; + fdata->num_files++; + } + else + { + /* + * In the unlikely event that we exceed MAX_FLUSH_BUFFERS, + * fall back to treating it as a standalone write. + */ + fdata = NULL; + } + } + } + + errno = 0; + pgstat_report_wait_start(WAIT_EVENT_SLRU_WRITE); + if (pg_pwrite(fd, shared->page_buffer[slotno], BLCKSZ, offset) != BLCKSZ) + { + pgstat_report_wait_end(); + /* if write didn't set errno, assume problem is no disk space */ + if (errno == 0) + errno = ENOSPC; + slru_errcause = SLRU_WRITE_FAILED; + slru_errno = errno; + if (!fdata) + CloseTransientFile(fd); + return false; + } + pgstat_report_wait_end(); + + /* Queue up a sync request for the checkpointer. */ + if (ctl->sync_handler != SYNC_HANDLER_NONE) + { + FileTag tag; + + INIT_SLRUFILETAG(tag, ctl->sync_handler, segno); + if (!RegisterSyncRequest(&tag, SYNC_REQUEST, false)) + { + /* No space to enqueue sync request. Do it synchronously. */ + pgstat_report_wait_start(WAIT_EVENT_SLRU_SYNC); + if (pg_fsync(fd) != 0) + { + pgstat_report_wait_end(); + slru_errcause = SLRU_FSYNC_FAILED; + slru_errno = errno; + CloseTransientFile(fd); + return false; + } + pgstat_report_wait_end(); + } + } + + /* Close file, unless part of flush request. */ + if (!fdata) + { + if (CloseTransientFile(fd) != 0) + { + slru_errcause = SLRU_CLOSE_FAILED; + slru_errno = errno; + return false; + } + } + + return true; +} + +/* + * Issue the error message after failure of SlruPhysicalReadPage or + * SlruPhysicalWritePage. Call this after cleaning up shared-memory state. + */ +static void +SlruReportIOError(SlruCtl ctl, int pageno, TransactionId xid) +{ + int segno = pageno / SLRU_PAGES_PER_SEGMENT; + int rpageno = pageno % SLRU_PAGES_PER_SEGMENT; + int offset = rpageno * BLCKSZ; + char path[MAXPGPATH]; + + SlruFileName(ctl, path, segno); + errno = slru_errno; + switch (slru_errcause) + { + case SLRU_OPEN_FAILED: + ereport(ERROR, + (errcode_for_file_access(), + errmsg("could not access status of transaction %u", xid), + errdetail("Could not open file \"%s\": %m.", path))); + break; + case SLRU_SEEK_FAILED: + ereport(ERROR, + (errcode_for_file_access(), + errmsg("could not access status of transaction %u", xid), + errdetail("Could not seek in file \"%s\" to offset %d: %m.", + path, offset))); + break; + case SLRU_READ_FAILED: + if (errno) + ereport(ERROR, + (errcode_for_file_access(), + errmsg("could not access status of transaction %u", xid), + errdetail("Could not read from file \"%s\" at offset %d: %m.", + path, offset))); + else + ereport(ERROR, + (errmsg("could not access status of transaction %u", xid), + errdetail("Could not read from file \"%s\" at offset %d: read too few bytes.", path, offset))); + break; + case SLRU_WRITE_FAILED: + if (errno) + ereport(ERROR, + (errcode_for_file_access(), + errmsg("could not access status of transaction %u", xid), + errdetail("Could not write to file \"%s\" at offset %d: %m.", + path, offset))); + else + ereport(ERROR, + (errmsg("could not access status of transaction %u", xid), + errdetail("Could not write to file \"%s\" at offset %d: wrote too few bytes.", + path, offset))); + break; + case SLRU_FSYNC_FAILED: + ereport(data_sync_elevel(ERROR), + (errcode_for_file_access(), + errmsg("could not access status of transaction %u", xid), + errdetail("Could not fsync file \"%s\": %m.", + path))); + break; + case SLRU_CLOSE_FAILED: + ereport(ERROR, + (errcode_for_file_access(), + errmsg("could not access status of transaction %u", xid), + errdetail("Could not close file \"%s\": %m.", + path))); + break; + default: + /* can't get here, we trust */ + elog(ERROR, "unrecognized SimpleLru error cause: %d", + (int) slru_errcause); + break; + } +} + +/* + * Select the slot to re-use when we need a free slot. + * + * The target page number is passed because we need to consider the + * possibility that some other process reads in the target page while + * we are doing I/O to free a slot. Hence, check or recheck to see if + * any slot already holds the target page, and return that slot if so. + * Thus, the returned slot is *either* a slot already holding the pageno + * (could be any state except EMPTY), *or* a freeable slot (state EMPTY + * or CLEAN). + * + * Control lock must be held at entry, and will be held at exit. + */ +static int +SlruSelectLRUPage(SlruCtl ctl, int pageno) +{ + SlruShared shared = ctl->shared; + + /* Outer loop handles restart after I/O */ + for (;;) + { + int slotno; + int cur_count; + int bestvalidslot = 0; /* keep compiler quiet */ + int best_valid_delta = -1; + int best_valid_page_number = 0; /* keep compiler quiet */ + int bestinvalidslot = 0; /* keep compiler quiet */ + int best_invalid_delta = -1; + int best_invalid_page_number = 0; /* keep compiler quiet */ + + /* See if page already has a buffer assigned */ + for (slotno = 0; slotno < shared->num_slots; slotno++) + { + if (shared->page_number[slotno] == pageno && + shared->page_status[slotno] != SLRU_PAGE_EMPTY) + return slotno; + } + + /* + * If we find any EMPTY slot, just select that one. Else choose a + * victim page to replace. We normally take the least recently used + * valid page, but we will never take the slot containing + * latest_page_number, even if it appears least recently used. We + * will select a slot that is already I/O busy only if there is no + * other choice: a read-busy slot will not be least recently used once + * the read finishes, and waiting for an I/O on a write-busy slot is + * inferior to just picking some other slot. Testing shows the slot + * we pick instead will often be clean, allowing us to begin a read at + * once. + * + * Normally the page_lru_count values will all be different and so + * there will be a well-defined LRU page. But since we allow + * concurrent execution of SlruRecentlyUsed() within + * SimpleLruReadPage_ReadOnly(), it is possible that multiple pages + * acquire the same lru_count values. In that case we break ties by + * choosing the furthest-back page. + * + * Notice that this next line forcibly advances cur_lru_count to a + * value that is certainly beyond any value that will be in the + * page_lru_count array after the loop finishes. This ensures that + * the next execution of SlruRecentlyUsed will mark the page newly + * used, even if it's for a page that has the current counter value. + * That gets us back on the path to having good data when there are + * multiple pages with the same lru_count. + */ + cur_count = (shared->cur_lru_count)++; + for (slotno = 0; slotno < shared->num_slots; slotno++) + { + int this_delta; + int this_page_number; + + if (shared->page_status[slotno] == SLRU_PAGE_EMPTY) + return slotno; + this_delta = cur_count - shared->page_lru_count[slotno]; + if (this_delta < 0) + { + /* + * Clean up in case shared updates have caused cur_count + * increments to get "lost". We back off the page counts, + * rather than trying to increase cur_count, to avoid any + * question of infinite loops or failure in the presence of + * wrapped-around counts. + */ + shared->page_lru_count[slotno] = cur_count; + this_delta = 0; + } + this_page_number = shared->page_number[slotno]; + if (this_page_number == shared->latest_page_number) + continue; + if (shared->page_status[slotno] == SLRU_PAGE_VALID) + { + if (this_delta > best_valid_delta || + (this_delta == best_valid_delta && + ctl->PagePrecedes(this_page_number, + best_valid_page_number))) + { + bestvalidslot = slotno; + best_valid_delta = this_delta; + best_valid_page_number = this_page_number; + } + } + else + { + if (this_delta > best_invalid_delta || + (this_delta == best_invalid_delta && + ctl->PagePrecedes(this_page_number, + best_invalid_page_number))) + { + bestinvalidslot = slotno; + best_invalid_delta = this_delta; + best_invalid_page_number = this_page_number; + } + } + } + + /* + * If all pages (except possibly the latest one) are I/O busy, we'll + * have to wait for an I/O to complete and then retry. In that + * unhappy case, we choose to wait for the I/O on the least recently + * used slot, on the assumption that it was likely initiated first of + * all the I/Os in progress and may therefore finish first. + */ + if (best_valid_delta < 0) + { + SimpleLruWaitIO(ctl, bestinvalidslot); + continue; + } + + /* + * If the selected page is clean, we're set. + */ + if (!shared->page_dirty[bestvalidslot]) + return bestvalidslot; + + /* + * Write the page. + */ + SlruInternalWritePage(ctl, bestvalidslot, NULL); + + /* + * Now loop back and try again. This is the easiest way of dealing + * with corner cases such as the victim page being re-dirtied while we + * wrote it. + */ + } +} + +/* + * Write dirty pages to disk during checkpoint or database shutdown. Flushing + * is deferred until the next call to ProcessSyncRequests(), though we do fsync + * the containing directory here to make sure that newly created directory + * entries are on disk. + */ +void +SimpleLruWriteAll(SlruCtl ctl, bool allow_redirtied) +{ + SlruShared shared = ctl->shared; + SlruWriteAllData fdata; + int slotno; + int pageno = 0; + int i; + bool ok; + + /* update the stats counter of flushes */ + pgstat_count_slru_flush(shared->slru_stats_idx); + + /* + * Find and write dirty pages + */ + fdata.num_files = 0; + + LWLockAcquire(shared->ControlLock, LW_EXCLUSIVE); + + for (slotno = 0; slotno < shared->num_slots; slotno++) + { + SlruInternalWritePage(ctl, slotno, &fdata); + + /* + * In some places (e.g. checkpoints), we cannot assert that the slot + * is clean now, since another process might have re-dirtied it + * already. That's okay. + */ + Assert(allow_redirtied || + shared->page_status[slotno] == SLRU_PAGE_EMPTY || + (shared->page_status[slotno] == SLRU_PAGE_VALID && + !shared->page_dirty[slotno])); + } + + LWLockRelease(shared->ControlLock); + + /* + * Now close any files that were open + */ + ok = true; + for (i = 0; i < fdata.num_files; i++) + { + if (CloseTransientFile(fdata.fd[i]) != 0) + { + slru_errcause = SLRU_CLOSE_FAILED; + slru_errno = errno; + pageno = fdata.segno[i] * SLRU_PAGES_PER_SEGMENT; + ok = false; + } + } + if (!ok) + SlruReportIOError(ctl, pageno, InvalidTransactionId); + + /* Ensure that directory entries for new files are on disk. */ + if (ctl->sync_handler != SYNC_HANDLER_NONE) + fsync_fname(ctl->Dir, true); +} + +/* + * Remove all segments before the one holding the passed page number + * + * All SLRUs prevent concurrent calls to this function, either with an LWLock + * or by calling it only as part of a checkpoint. Mutual exclusion must begin + * before computing cutoffPage. Mutual exclusion must end after any limit + * update that would permit other backends to write fresh data into the + * segment immediately preceding the one containing cutoffPage. Otherwise, + * when the SLRU is quite full, SimpleLruTruncate() might delete that segment + * after it has accrued freshly-written data. + */ +void +SimpleLruTruncate(SlruCtl ctl, int cutoffPage) +{ + SlruShared shared = ctl->shared; + int slotno; + + /* update the stats counter of truncates */ + pgstat_count_slru_truncate(shared->slru_stats_idx); + + /* + * Scan shared memory and remove any pages preceding the cutoff page, to + * ensure we won't rewrite them later. (Since this is normally called in + * or just after a checkpoint, any dirty pages should have been flushed + * already ... we're just being extra careful here.) + */ + LWLockAcquire(shared->ControlLock, LW_EXCLUSIVE); + +restart:; + + /* + * While we are holding the lock, make an important safety check: the + * current endpoint page must not be eligible for removal. + */ + if (ctl->PagePrecedes(shared->latest_page_number, cutoffPage)) + { + LWLockRelease(shared->ControlLock); + ereport(LOG, + (errmsg("could not truncate directory \"%s\": apparent wraparound", + ctl->Dir))); + return; + } + + for (slotno = 0; slotno < shared->num_slots; slotno++) + { + if (shared->page_status[slotno] == SLRU_PAGE_EMPTY) + continue; + if (!ctl->PagePrecedes(shared->page_number[slotno], cutoffPage)) + continue; + + /* + * If page is clean, just change state to EMPTY (expected case). + */ + if (shared->page_status[slotno] == SLRU_PAGE_VALID && + !shared->page_dirty[slotno]) + { + shared->page_status[slotno] = SLRU_PAGE_EMPTY; + continue; + } + + /* + * Hmm, we have (or may have) I/O operations acting on the page, so + * we've got to wait for them to finish and then start again. This is + * the same logic as in SlruSelectLRUPage. (XXX if page is dirty, + * wouldn't it be OK to just discard it without writing it? + * SlruMayDeleteSegment() uses a stricter qualification, so we might + * not delete this page in the end; even if we don't delete it, we + * won't have cause to read its data again. For now, keep the logic + * the same as it was.) + */ + if (shared->page_status[slotno] == SLRU_PAGE_VALID) + SlruInternalWritePage(ctl, slotno, NULL); + else + SimpleLruWaitIO(ctl, slotno); + goto restart; + } + + LWLockRelease(shared->ControlLock); + + /* Now we can remove the old segment(s) */ + (void) SlruScanDirectory(ctl, SlruScanDirCbDeleteCutoff, &cutoffPage); +} + +/* + * Delete an individual SLRU segment. + * + * NB: This does not touch the SLRU buffers themselves, callers have to ensure + * they either can't yet contain anything, or have already been cleaned out. + */ +static void +SlruInternalDeleteSegment(SlruCtl ctl, int segno) +{ + char path[MAXPGPATH]; + + /* Forget any fsync requests queued for this segment. */ + if (ctl->sync_handler != SYNC_HANDLER_NONE) + { + FileTag tag; + + INIT_SLRUFILETAG(tag, ctl->sync_handler, segno); + RegisterSyncRequest(&tag, SYNC_FORGET_REQUEST, true); + } + + /* Unlink the file. */ + SlruFileName(ctl, path, segno); + ereport(DEBUG2, (errmsg_internal("removing file \"%s\"", path))); + unlink(path); +} + +/* + * Delete an individual SLRU segment, identified by the segment number. + */ +void +SlruDeleteSegment(SlruCtl ctl, int segno) +{ + SlruShared shared = ctl->shared; + int slotno; + bool did_write; + + /* Clean out any possibly existing references to the segment. */ + LWLockAcquire(shared->ControlLock, LW_EXCLUSIVE); +restart: + did_write = false; + for (slotno = 0; slotno < shared->num_slots; slotno++) + { + int pagesegno = shared->page_number[slotno] / SLRU_PAGES_PER_SEGMENT; + + if (shared->page_status[slotno] == SLRU_PAGE_EMPTY) + continue; + + /* not the segment we're looking for */ + if (pagesegno != segno) + continue; + + /* If page is clean, just change state to EMPTY (expected case). */ + if (shared->page_status[slotno] == SLRU_PAGE_VALID && + !shared->page_dirty[slotno]) + { + shared->page_status[slotno] = SLRU_PAGE_EMPTY; + continue; + } + + /* Same logic as SimpleLruTruncate() */ + if (shared->page_status[slotno] == SLRU_PAGE_VALID) + SlruInternalWritePage(ctl, slotno, NULL); + else + SimpleLruWaitIO(ctl, slotno); + + did_write = true; + } + + /* + * Be extra careful and re-check. The IO functions release the control + * lock, so new pages could have been read in. + */ + if (did_write) + goto restart; + + SlruInternalDeleteSegment(ctl, segno); + + LWLockRelease(shared->ControlLock); +} + +/* + * Determine whether a segment is okay to delete. + * + * segpage is the first page of the segment, and cutoffPage is the oldest (in + * PagePrecedes order) page in the SLRU containing still-useful data. Since + * every core PagePrecedes callback implements "wrap around", check the + * segment's first and last pages: + * + * first<cutoff && last<cutoff: yes + * first<cutoff && last>=cutoff: no; cutoff falls inside this segment + * first>=cutoff && last<cutoff: no; wrap point falls inside this segment + * first>=cutoff && last>=cutoff: no; every page of this segment is too young + */ +static bool +SlruMayDeleteSegment(SlruCtl ctl, int segpage, int cutoffPage) +{ + int seg_last_page = segpage + SLRU_PAGES_PER_SEGMENT - 1; + + Assert(segpage % SLRU_PAGES_PER_SEGMENT == 0); + + return (ctl->PagePrecedes(segpage, cutoffPage) && + ctl->PagePrecedes(seg_last_page, cutoffPage)); +} + +#ifdef USE_ASSERT_CHECKING +static void +SlruPagePrecedesTestOffset(SlruCtl ctl, int per_page, uint32 offset) +{ + TransactionId lhs, + rhs; + int newestPage, + oldestPage; + TransactionId newestXact, + oldestXact; + + /* + * Compare an XID pair having undefined order (see RFC 1982), a pair at + * "opposite ends" of the XID space. TransactionIdPrecedes() treats each + * as preceding the other. If RHS is oldestXact, LHS is the first XID we + * must not assign. + */ + lhs = per_page + offset; /* skip first page to avoid non-normal XIDs */ + rhs = lhs + (1U << 31); + Assert(TransactionIdPrecedes(lhs, rhs)); + Assert(TransactionIdPrecedes(rhs, lhs)); + Assert(!TransactionIdPrecedes(lhs - 1, rhs)); + Assert(TransactionIdPrecedes(rhs, lhs - 1)); + Assert(TransactionIdPrecedes(lhs + 1, rhs)); + Assert(!TransactionIdPrecedes(rhs, lhs + 1)); + Assert(!TransactionIdFollowsOrEquals(lhs, rhs)); + Assert(!TransactionIdFollowsOrEquals(rhs, lhs)); + Assert(!ctl->PagePrecedes(lhs / per_page, lhs / per_page)); + Assert(!ctl->PagePrecedes(lhs / per_page, rhs / per_page)); + Assert(!ctl->PagePrecedes(rhs / per_page, lhs / per_page)); + Assert(!ctl->PagePrecedes((lhs - per_page) / per_page, rhs / per_page)); + Assert(ctl->PagePrecedes(rhs / per_page, (lhs - 3 * per_page) / per_page)); + Assert(ctl->PagePrecedes(rhs / per_page, (lhs - 2 * per_page) / per_page)); + Assert(ctl->PagePrecedes(rhs / per_page, (lhs - 1 * per_page) / per_page) + || (1U << 31) % per_page != 0); /* See CommitTsPagePrecedes() */ + Assert(ctl->PagePrecedes((lhs + 1 * per_page) / per_page, rhs / per_page) + || (1U << 31) % per_page != 0); + Assert(ctl->PagePrecedes((lhs + 2 * per_page) / per_page, rhs / per_page)); + Assert(ctl->PagePrecedes((lhs + 3 * per_page) / per_page, rhs / per_page)); + Assert(!ctl->PagePrecedes(rhs / per_page, (lhs + per_page) / per_page)); + + /* + * GetNewTransactionId() has assigned the last XID it can safely use, and + * that XID is in the *LAST* page of the second segment. We must not + * delete that segment. + */ + newestPage = 2 * SLRU_PAGES_PER_SEGMENT - 1; + newestXact = newestPage * per_page + offset; + Assert(newestXact / per_page == newestPage); + oldestXact = newestXact + 1; + oldestXact -= 1U << 31; + oldestPage = oldestXact / per_page; + Assert(!SlruMayDeleteSegment(ctl, + (newestPage - + newestPage % SLRU_PAGES_PER_SEGMENT), + oldestPage)); + + /* + * GetNewTransactionId() has assigned the last XID it can safely use, and + * that XID is in the *FIRST* page of the second segment. We must not + * delete that segment. + */ + newestPage = SLRU_PAGES_PER_SEGMENT; + newestXact = newestPage * per_page + offset; + Assert(newestXact / per_page == newestPage); + oldestXact = newestXact + 1; + oldestXact -= 1U << 31; + oldestPage = oldestXact / per_page; + Assert(!SlruMayDeleteSegment(ctl, + (newestPage - + newestPage % SLRU_PAGES_PER_SEGMENT), + oldestPage)); +} + +/* + * Unit-test a PagePrecedes function. + * + * This assumes every uint32 >= FirstNormalTransactionId is a valid key. It + * assumes each value occupies a contiguous, fixed-size region of SLRU bytes. + * (MultiXactMemberCtl separates flags from XIDs. AsyncCtl has + * variable-length entries, no keys, and no random access. These unit tests + * do not apply to them.) + */ +void +SlruPagePrecedesUnitTests(SlruCtl ctl, int per_page) +{ + /* Test first, middle and last entries of a page. */ + SlruPagePrecedesTestOffset(ctl, per_page, 0); + SlruPagePrecedesTestOffset(ctl, per_page, per_page / 2); + SlruPagePrecedesTestOffset(ctl, per_page, per_page - 1); +} +#endif + +/* + * SlruScanDirectory callback + * This callback reports true if there's any segment wholly prior to the + * one containing the page passed as "data". + */ +bool +SlruScanDirCbReportPresence(SlruCtl ctl, char *filename, int segpage, void *data) +{ + int cutoffPage = *(int *) data; + + if (SlruMayDeleteSegment(ctl, segpage, cutoffPage)) + return true; /* found one; don't iterate any more */ + + return false; /* keep going */ +} + +/* + * SlruScanDirectory callback. + * This callback deletes segments prior to the one passed in as "data". + */ +static bool +SlruScanDirCbDeleteCutoff(SlruCtl ctl, char *filename, int segpage, void *data) +{ + int cutoffPage = *(int *) data; + + if (SlruMayDeleteSegment(ctl, segpage, cutoffPage)) + SlruInternalDeleteSegment(ctl, segpage / SLRU_PAGES_PER_SEGMENT); + + return false; /* keep going */ +} + +/* + * SlruScanDirectory callback. + * This callback deletes all segments. + */ +bool +SlruScanDirCbDeleteAll(SlruCtl ctl, char *filename, int segpage, void *data) +{ + SlruInternalDeleteSegment(ctl, segpage / SLRU_PAGES_PER_SEGMENT); + + return false; /* keep going */ +} + +/* + * Scan the SimpleLru directory and apply a callback to each file found in it. + * + * If the callback returns true, the scan is stopped. The last return value + * from the callback is returned. + * + * The callback receives the following arguments: 1. the SlruCtl struct for the + * slru being truncated; 2. the filename being considered; 3. the page number + * for the first page of that file; 4. a pointer to the opaque data given to us + * by the caller. + * + * Note that the ordering in which the directory is scanned is not guaranteed. + * + * Note that no locking is applied. + */ +bool +SlruScanDirectory(SlruCtl ctl, SlruScanCallback callback, void *data) +{ + bool retval = false; + DIR *cldir; + struct dirent *clde; + int segno; + int segpage; + + cldir = AllocateDir(ctl->Dir); + while ((clde = ReadDir(cldir, ctl->Dir)) != NULL) + { + size_t len; + + len = strlen(clde->d_name); + + if ((len == 4 || len == 5 || len == 6) && + strspn(clde->d_name, "0123456789ABCDEF") == len) + { + segno = (int) strtol(clde->d_name, NULL, 16); + segpage = segno * SLRU_PAGES_PER_SEGMENT; + + elog(DEBUG2, "SlruScanDirectory invoking callback on %s/%s", + ctl->Dir, clde->d_name); + retval = callback(ctl, clde->d_name, segpage, data); + if (retval) + break; + } + } + FreeDir(cldir); + + return retval; +} + +/* + * Individual SLRUs (clog, ...) have to provide a sync.c handler function so + * that they can provide the correct "SlruCtl" (otherwise we don't know how to + * build the path), but they just forward to this common implementation that + * performs the fsync. + */ +int +SlruSyncFileTag(SlruCtl ctl, const FileTag *ftag, char *path) +{ + int fd; + int save_errno; + int result; + + SlruFileName(ctl, path, ftag->segno); + + fd = OpenTransientFile(path, O_RDWR | PG_BINARY); + if (fd < 0) + return -1; + + pgstat_report_wait_start(WAIT_EVENT_SLRU_FLUSH_SYNC); + result = pg_fsync(fd); + pgstat_report_wait_end(); + save_errno = errno; + + CloseTransientFile(fd); + + errno = save_errno; + return result; +} |