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Diffstat (limited to 'src/backend/access/transam/clog.c')
| -rw-r--r-- | src/backend/access/transam/clog.c | 1009 |
1 files changed, 0 insertions, 1009 deletions
diff --git a/src/backend/access/transam/clog.c b/src/backend/access/transam/clog.c deleted file mode 100644 index ffd9ef3fcbd..00000000000 --- a/src/backend/access/transam/clog.c +++ /dev/null @@ -1,1009 +0,0 @@ -/*------------------------------------------------------------------------- - * - * clog.c - * PostgreSQL transaction-commit-log manager - * - * This module replaces the old "pg_log" access code, which treated pg_log - * essentially like a relation, in that it went through the regular buffer - * manager. The problem with that was that there wasn't any good way to - * recycle storage space for transactions so old that they'll never be - * looked up again. Now we use specialized access code so that the commit - * log can be broken into relatively small, independent segments. - * - * Portions Copyright (c) 1996-2002, PostgreSQL Global Development Group - * Portions Copyright (c) 1994, Regents of the University of California - * - * $Header: /cvsroot/pgsql/src/backend/access/transam/clog.c,v 1.9 2002/06/20 20:29:25 momjian Exp $ - * - *------------------------------------------------------------------------- - */ -#include "postgres.h" - -#include <fcntl.h> -#include <dirent.h> -#include <errno.h> -#include <sys/stat.h> -#include <sys/types.h> -#include <unistd.h> - -#include "access/clog.h" -#include "storage/lwlock.h" -#include "miscadmin.h" - - -/* - * Defines for CLOG page and segment sizes. A page is the same BLCKSZ - * as is used everywhere else in Postgres. The CLOG segment size can be - * chosen somewhat arbitrarily; we make it 1 million transactions by default, - * or 256Kb. - * - * Note: because TransactionIds are 32 bits and wrap around at 0xFFFFFFFF, - * CLOG page numbering also wraps around at 0xFFFFFFFF/CLOG_XACTS_PER_PAGE, - * and CLOG segment numbering at 0xFFFFFFFF/CLOG_XACTS_PER_SEGMENT. We need - * take no explicit notice of that fact in this module, except when comparing - * segment and page numbers in TruncateCLOG (see CLOGPagePrecedes). - */ - -#define CLOG_BLCKSZ BLCKSZ - -/* We need two bits per xact, so four xacts fit in a byte */ -#define CLOG_BITS_PER_XACT 2 -#define CLOG_XACTS_PER_BYTE 4 -#define CLOG_XACTS_PER_PAGE (CLOG_BLCKSZ * CLOG_XACTS_PER_BYTE) -#define CLOG_XACT_BITMASK ((1 << CLOG_BITS_PER_XACT) - 1) - -#define CLOG_XACTS_PER_SEGMENT 0x100000 -#define CLOG_PAGES_PER_SEGMENT (CLOG_XACTS_PER_SEGMENT / CLOG_XACTS_PER_PAGE) - -#define TransactionIdToPage(xid) ((xid) / (TransactionId) CLOG_XACTS_PER_PAGE) -#define TransactionIdToPgIndex(xid) ((xid) % (TransactionId) CLOG_XACTS_PER_PAGE) -#define TransactionIdToByte(xid) (TransactionIdToPgIndex(xid) / CLOG_XACTS_PER_BYTE) -#define TransactionIdToBIndex(xid) ((xid) % (TransactionId) CLOG_XACTS_PER_BYTE) - - -/*---------- - * Shared-memory data structures for CLOG control - * - * We use a simple least-recently-used scheme to manage a pool of page - * buffers for the CLOG. Under ordinary circumstances we expect that write - * traffic will occur mostly to the latest CLOG 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 an overall LWLock to protect the shared data structures, plus - * per-buffer LWLocks that synchronize I/O for each buffer. 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. - * - * To change the page number or state of a buffer, one must normally hold - * the control lock. (The sole exception to this rule is that a writer - * process changes the state from DIRTY to WRITE_IN_PROGRESS while holding - * only the per-buffer lock.) If the buffer's state is neither EMPTY nor - * CLEAN, then there may be processes doing (or waiting to do) I/O on the - * buffer, so the page number may not be changed, and the only allowed state - * transition is to change WRITE_IN_PROGRESS to DIRTY after dirtying the page. - * To do any other state transition involving a buffer with potential I/O - * processes, one must hold both the per-buffer lock and the control lock. - * (Note the control lock must be acquired second; do not wait on a buffer - * lock while holding the control lock.) A process wishing to read a page - * marks the buffer state as READ_IN_PROGRESS, then drops the control lock, - * acquires the per-buffer lock, and rechecks the state before proceeding. - * This recheck takes care of the possibility that someone else already did - * the read, while the early marking prevents someone else from trying to - * read the same page into a different buffer. - * - * Note we are assuming that read and write of the state value is atomic, - * since I/O processes may examine and change the state while not holding - * the control 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 setting the page's state from WRITE_IN_PROGRESS to DIRTY. The writing - * process must notice this and not mark the page CLEAN when it's done. - * - * XLOG interactions: this module generates an XLOG record whenever a new - * CLOG page is initialized to zeroes. Other writes of CLOG come from - * recording of transaction commit or abort in xact.c, which generates its - * own XLOG records for these events and will re-perform the status update - * on redo; so we need make no additional XLOG entry here. Also, the XLOG - * is guaranteed flushed through the XLOG commit record before we are called - * to log a commit, so the WAL rule "write xlog before data" is satisfied - * automatically for commits, and we don't really care for aborts. Therefore, - * we don't need to mark XLOG pages with LSN information; we have enough - * synchronization already. - *---------- - */ - -typedef enum -{ - CLOG_PAGE_EMPTY, /* CLOG buffer is not in use */ - CLOG_PAGE_READ_IN_PROGRESS, /* CLOG page is being read in */ - CLOG_PAGE_CLEAN, /* CLOG page is valid and not dirty */ - CLOG_PAGE_DIRTY, /* CLOG page is valid but needs write */ - CLOG_PAGE_WRITE_IN_PROGRESS /* CLOG page is being written out in */ -} ClogPageStatus; - -/* - * Shared-memory state for CLOG. - */ -typedef struct ClogCtlData -{ - /* - * Info for each buffer slot. Page number is undefined when status is - * EMPTY. lru_count is essentially the number of operations since - * last use of this page; the page with highest lru_count is the best - * candidate to replace. - */ - char *page_buffer[NUM_CLOG_BUFFERS]; - ClogPageStatus page_status[NUM_CLOG_BUFFERS]; - int page_number[NUM_CLOG_BUFFERS]; - unsigned int page_lru_count[NUM_CLOG_BUFFERS]; - - /* - * latest_page_number is the page number of the current end of the - * CLOG; this is not critical data, since we use it only to avoid - * swapping out the latest page. - */ - int latest_page_number; -} ClogCtlData; - -static ClogCtlData *ClogCtl = NULL; - -/* - * ClogBufferLocks is set during CLOGShmemInit and does not change thereafter. - * The value is automatically inherited by backends via fork, and - * doesn't need to be in shared memory. - */ -static LWLockId ClogBufferLocks[NUM_CLOG_BUFFERS]; /* Per-buffer I/O locks */ - -/* - * ClogDir is set during CLOGShmemInit and does not change thereafter. - * The value is automatically inherited by backends via fork, and - * doesn't need to be in shared memory. - */ -static char ClogDir[MAXPGPATH]; - -#define ClogFileName(path, seg) \ - snprintf(path, MAXPGPATH, "%s/%04X", ClogDir, seg) - -/* - * Macro to mark a buffer slot "most recently used". - */ -#define ClogRecentlyUsed(slotno) \ - do { \ - int iilru; \ - for (iilru = 0; iilru < NUM_CLOG_BUFFERS; iilru++) \ - ClogCtl->page_lru_count[iilru]++; \ - ClogCtl->page_lru_count[slotno] = 0; \ - } while (0) - - -static int ZeroCLOGPage(int pageno, bool writeXlog); -static int ReadCLOGPage(int pageno); -static void WriteCLOGPage(int slotno); -static void CLOGPhysicalReadPage(int pageno, int slotno); -static void CLOGPhysicalWritePage(int pageno, int slotno); -static int SelectLRUCLOGPage(int pageno); -static bool ScanCLOGDirectory(int cutoffPage, bool doDeletions); -static bool CLOGPagePrecedes(int page1, int page2); -static void WriteZeroPageXlogRec(int pageno); - - -/* - * Record the final state of a transaction in the commit log. - * - * NB: this is a low-level routine and is NOT the preferred entry point - * for most uses; TransactionLogUpdate() in transam.c is the intended caller. - */ -void -TransactionIdSetStatus(TransactionId xid, XidStatus status) -{ - int pageno = TransactionIdToPage(xid); - int byteno = TransactionIdToByte(xid); - int bshift = TransactionIdToBIndex(xid) * CLOG_BITS_PER_XACT; - int slotno; - char *byteptr; - - Assert(status == TRANSACTION_STATUS_COMMITTED || - status == TRANSACTION_STATUS_ABORTED); - - LWLockAcquire(CLogControlLock, LW_EXCLUSIVE); - - slotno = ReadCLOGPage(pageno); - byteptr = ClogCtl->page_buffer[slotno] + byteno; - - /* Current state should be 0 or target state */ - Assert(((*byteptr >> bshift) & CLOG_XACT_BITMASK) == 0 || - ((*byteptr >> bshift) & CLOG_XACT_BITMASK) == status); - - *byteptr |= (status << bshift); - - ClogCtl->page_status[slotno] = CLOG_PAGE_DIRTY; - - LWLockRelease(CLogControlLock); -} - -/* - * Interrogate the state of a transaction in the commit log. - * - * NB: this is a low-level routine and is NOT the preferred entry point - * for most uses; TransactionLogTest() in transam.c is the intended caller. - */ -XidStatus -TransactionIdGetStatus(TransactionId xid) -{ - int pageno = TransactionIdToPage(xid); - int byteno = TransactionIdToByte(xid); - int bshift = TransactionIdToBIndex(xid) * CLOG_BITS_PER_XACT; - int slotno; - char *byteptr; - XidStatus status; - - LWLockAcquire(CLogControlLock, LW_EXCLUSIVE); - - slotno = ReadCLOGPage(pageno); - byteptr = ClogCtl->page_buffer[slotno] + byteno; - - status = (*byteptr >> bshift) & CLOG_XACT_BITMASK; - - LWLockRelease(CLogControlLock); - - return status; -} - - -/* - * Initialization of shared memory for CLOG - */ - -int -CLOGShmemSize(void) -{ - return MAXALIGN(sizeof(ClogCtlData) + CLOG_BLCKSZ * NUM_CLOG_BUFFERS); -} - -void -CLOGShmemInit(void) -{ - bool found; - char *bufptr; - int slotno; - - /* this must agree with space requested by CLOGShmemSize() */ - ClogCtl = (ClogCtlData *) - ShmemInitStruct("CLOG Ctl", - MAXALIGN(sizeof(ClogCtlData) + - CLOG_BLCKSZ * NUM_CLOG_BUFFERS), - &found); - Assert(!found); - - memset(ClogCtl, 0, sizeof(ClogCtlData)); - - bufptr = ((char *) ClogCtl) + sizeof(ClogCtlData); - - for (slotno = 0; slotno < NUM_CLOG_BUFFERS; slotno++) - { - ClogCtl->page_buffer[slotno] = bufptr; - ClogCtl->page_status[slotno] = CLOG_PAGE_EMPTY; - ClogBufferLocks[slotno] = LWLockAssign(); - bufptr += CLOG_BLCKSZ; - } - - /* ClogCtl->latest_page_number will be set later */ - - /* Init CLOG directory path */ - snprintf(ClogDir, MAXPGPATH, "%s/pg_clog", DataDir); -} - -/* - * This func must be called ONCE on system install. It creates - * the initial CLOG segment. (The CLOG directory is assumed to - * have been created by the initdb shell script, and CLOGShmemInit - * must have been called already.) - */ -void -BootStrapCLOG(void) -{ - int slotno; - - LWLockAcquire(CLogControlLock, LW_EXCLUSIVE); - - /* Create and zero the first page of the commit log */ - slotno = ZeroCLOGPage(0, false); - - /* Make sure it's written out */ - WriteCLOGPage(slotno); - Assert(ClogCtl->page_status[slotno] == CLOG_PAGE_CLEAN); - - LWLockRelease(CLogControlLock); -} - -/* - * Initialize (or reinitialize) a page of CLOG to zeroes. - * If writeXlog is TRUE, also emit an XLOG record saying we did this. - * - * 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. - */ -static int -ZeroCLOGPage(int pageno, bool writeXlog) -{ - int slotno; - - /* Find a suitable buffer slot for the page */ - slotno = SelectLRUCLOGPage(pageno); - Assert(ClogCtl->page_status[slotno] == CLOG_PAGE_EMPTY || - ClogCtl->page_status[slotno] == CLOG_PAGE_CLEAN || - ClogCtl->page_number[slotno] == pageno); - - /* Mark the slot as containing this page */ - ClogCtl->page_number[slotno] = pageno; - ClogCtl->page_status[slotno] = CLOG_PAGE_DIRTY; - ClogRecentlyUsed(slotno); - - /* Set the buffer to zeroes */ - MemSet(ClogCtl->page_buffer[slotno], 0, CLOG_BLCKSZ); - - /* Assume this page is now the latest active page */ - ClogCtl->latest_page_number = pageno; - - if (writeXlog) - WriteZeroPageXlogRec(pageno); - - return slotno; -} - -/* - * Find a CLOG page in a shared buffer, reading it in if necessary. - * The page number must correspond to an already-initialized page. - * - * 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. - */ -static int -ReadCLOGPage(int pageno) -{ - /* Outer loop handles restart if we lose the buffer to someone else */ - for (;;) - { - int slotno; - - /* See if page already is in memory; if not, pick victim slot */ - slotno = SelectLRUCLOGPage(pageno); - - /* Did we find the page in memory? */ - if (ClogCtl->page_number[slotno] == pageno && - ClogCtl->page_status[slotno] != CLOG_PAGE_EMPTY) - { - /* If page is still being read in, we cannot use it yet */ - if (ClogCtl->page_status[slotno] != CLOG_PAGE_READ_IN_PROGRESS) - { - /* otherwise, it's ready to use */ - ClogRecentlyUsed(slotno); - return slotno; - } - } - else - { - /* We found no match; assert we selected a freeable slot */ - Assert(ClogCtl->page_status[slotno] == CLOG_PAGE_EMPTY || - ClogCtl->page_status[slotno] == CLOG_PAGE_CLEAN); - } - - /* Mark the slot read-busy (no-op if it already was) */ - ClogCtl->page_number[slotno] = pageno; - ClogCtl->page_status[slotno] = CLOG_PAGE_READ_IN_PROGRESS; - - /* - * Temporarily mark page as recently-used to discourage - * SelectLRUCLOGPage from selecting it again for someone else. - */ - ClogCtl->page_lru_count[slotno] = 0; - - /* Release shared lock, grab per-buffer lock instead */ - LWLockRelease(CLogControlLock); - LWLockAcquire(ClogBufferLocks[slotno], LW_EXCLUSIVE); - - /* - * Check to see if someone else already did the read, or took the - * buffer away from us. If so, restart from the top. - */ - if (ClogCtl->page_number[slotno] != pageno || - ClogCtl->page_status[slotno] != CLOG_PAGE_READ_IN_PROGRESS) - { - LWLockRelease(ClogBufferLocks[slotno]); - LWLockAcquire(CLogControlLock, LW_EXCLUSIVE); - continue; - } - - /* Okay, do the read */ - CLOGPhysicalReadPage(pageno, slotno); - - /* Re-acquire shared control lock and update page state */ - LWLockAcquire(CLogControlLock, LW_EXCLUSIVE); - - Assert(ClogCtl->page_number[slotno] == pageno && - ClogCtl->page_status[slotno] == CLOG_PAGE_READ_IN_PROGRESS); - - ClogCtl->page_status[slotno] = CLOG_PAGE_CLEAN; - - LWLockRelease(ClogBufferLocks[slotno]); - - ClogRecentlyUsed(slotno); - return slotno; - } -} - -/* - * Write a CLOG 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 -WriteCLOGPage(int slotno) -{ - int pageno; - - /* Do nothing if page does not need writing */ - if (ClogCtl->page_status[slotno] != CLOG_PAGE_DIRTY && - ClogCtl->page_status[slotno] != CLOG_PAGE_WRITE_IN_PROGRESS) - return; - - pageno = ClogCtl->page_number[slotno]; - - /* Release shared lock, grab per-buffer lock instead */ - LWLockRelease(CLogControlLock); - LWLockAcquire(ClogBufferLocks[slotno], LW_EXCLUSIVE); - - /* - * Check to see if someone else already did the write, or took the - * buffer away from us. If so, do nothing. NOTE: we really should - * never see WRITE_IN_PROGRESS here, since that state should only - * occur while the writer is holding the buffer lock. But accept it - * so that we have a recovery path if a writer aborts. - */ - if (ClogCtl->page_number[slotno] != pageno || - (ClogCtl->page_status[slotno] != CLOG_PAGE_DIRTY && - ClogCtl->page_status[slotno] != CLOG_PAGE_WRITE_IN_PROGRESS)) - { - LWLockRelease(ClogBufferLocks[slotno]); - LWLockAcquire(CLogControlLock, LW_EXCLUSIVE); - return; - } - - /* - * Mark the slot write-busy. After this point, a transaction status - * update on this page will mark it dirty again. NB: we are assuming - * that read/write of the page status field is atomic, since we change - * the state while not holding control lock. However, we cannot set - * this state any sooner, or we'd possibly fool a previous writer into - * thinking he's successfully dumped the page when he hasn't. - * (Scenario: other writer starts, page is redirtied, we come along - * and set WRITE_IN_PROGRESS again, other writer completes and sets - * CLEAN because redirty info has been lost, then we think it's clean - * too.) - */ - ClogCtl->page_status[slotno] = CLOG_PAGE_WRITE_IN_PROGRESS; - - /* Okay, do the write */ - CLOGPhysicalWritePage(pageno, slotno); - - /* Re-acquire shared control lock and update page state */ - LWLockAcquire(CLogControlLock, LW_EXCLUSIVE); - - Assert(ClogCtl->page_number[slotno] == pageno && - (ClogCtl->page_status[slotno] == CLOG_PAGE_WRITE_IN_PROGRESS || - ClogCtl->page_status[slotno] == CLOG_PAGE_DIRTY)); - - /* Cannot set CLEAN if someone re-dirtied page since write started */ - if (ClogCtl->page_status[slotno] == CLOG_PAGE_WRITE_IN_PROGRESS) - ClogCtl->page_status[slotno] = CLOG_PAGE_CLEAN; - - LWLockRelease(ClogBufferLocks[slotno]); -} - -/* - * Physical read of a (previously existing) page into a buffer slot - * - * For now, assume it's not worth keeping a file pointer open across - * read/write operations. We could cache one virtual file pointer ... - */ -static void -CLOGPhysicalReadPage(int pageno, int slotno) -{ - int segno = pageno / CLOG_PAGES_PER_SEGMENT; - int rpageno = pageno % CLOG_PAGES_PER_SEGMENT; - int offset = rpageno * CLOG_BLCKSZ; - char path[MAXPGPATH]; - int fd; - - ClogFileName(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 - * CLOGPhysicalWritePage). Hence, if we are InRecovery, allow the - * case where the file doesn't exist, and return zeroes instead. - */ - fd = BasicOpenFile(path, O_RDWR | PG_BINARY, S_IRUSR | S_IWUSR); - if (fd < 0) - { - if (errno != ENOENT || !InRecovery) - elog(PANIC, "open of %s failed: %m", path); - elog(LOG, "clog file %s doesn't exist, reading as zeroes", path); - MemSet(ClogCtl->page_buffer[slotno], 0, CLOG_BLCKSZ); - return; - } - - if (lseek(fd, (off_t) offset, SEEK_SET) < 0) - elog(PANIC, "lseek of clog file %u, offset %u failed: %m", - segno, offset); - - errno = 0; - if (read(fd, ClogCtl->page_buffer[slotno], CLOG_BLCKSZ) != CLOG_BLCKSZ) - elog(PANIC, "read of clog file %u, offset %u failed: %m", - segno, offset); - - close(fd); -} - -/* - * Physical write of a page from a buffer slot - * - * For now, assume it's not worth keeping a file pointer open across - * read/write operations. We could cache one virtual file pointer ... - */ -static void -CLOGPhysicalWritePage(int pageno, int slotno) -{ - int segno = pageno / CLOG_PAGES_PER_SEGMENT; - int rpageno = pageno % CLOG_PAGES_PER_SEGMENT; - int offset = rpageno * CLOG_BLCKSZ; - char path[MAXPGPATH]; - int fd; - - ClogFileName(path, segno); - - /* - * 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 - * ZeroCLOGPage 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 CLOGPhysicalReadPage.) - */ - fd = BasicOpenFile(path, O_RDWR | PG_BINARY, S_IRUSR | S_IWUSR); - if (fd < 0) - { - if (errno != ENOENT) - elog(PANIC, "open of %s failed: %m", path); - fd = BasicOpenFile(path, O_RDWR | O_CREAT | O_EXCL | PG_BINARY, - S_IRUSR | S_IWUSR); - if (fd < 0) - elog(PANIC, "creation of file %s failed: %m", path); - } - - if (lseek(fd, (off_t) offset, SEEK_SET) < 0) - elog(PANIC, "lseek of clog file %u, offset %u failed: %m", - segno, offset); - - errno = 0; - if (write(fd, ClogCtl->page_buffer[slotno], CLOG_BLCKSZ) != CLOG_BLCKSZ) - { - /* if write didn't set errno, assume problem is no disk space */ - if (errno == 0) - errno = ENOSPC; - elog(PANIC, "write of clog file %u, offset %u failed: %m", - segno, offset); - } - - close(fd); -} - -/* - * 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 -SelectLRUCLOGPage(int pageno) -{ - /* Outer loop handles restart after I/O */ - for (;;) - { - int slotno; - int bestslot = 0; - unsigned int bestcount = 0; - - /* See if page already has a buffer assigned */ - for (slotno = 0; slotno < NUM_CLOG_BUFFERS; slotno++) - { - if (ClogCtl->page_number[slotno] == pageno && - ClogCtl->page_status[slotno] != CLOG_PAGE_EMPTY) - return slotno; - } - - /* - * If we find any EMPTY slot, just select that one. Else locate - * the least-recently-used slot that isn't the latest CLOG page. - */ - for (slotno = 0; slotno < NUM_CLOG_BUFFERS; slotno++) - { - if (ClogCtl->page_status[slotno] == CLOG_PAGE_EMPTY) - return slotno; - if (ClogCtl->page_lru_count[slotno] > bestcount && - ClogCtl->page_number[slotno] != ClogCtl->latest_page_number) - { - bestslot = slotno; - bestcount = ClogCtl->page_lru_count[slotno]; - } - } - - /* - * If the selected page is clean, we're set. - */ - if (ClogCtl->page_status[bestslot] == CLOG_PAGE_CLEAN) - return bestslot; - - /* - * We need to do I/O. Normal case is that we have to write it - * out, but it's possible in the worst case to have selected a - * read-busy page. In that case we use ReadCLOGPage to wait for - * the read to complete. - */ - if (ClogCtl->page_status[bestslot] == CLOG_PAGE_READ_IN_PROGRESS) - (void) ReadCLOGPage(ClogCtl->page_number[bestslot]); - else - WriteCLOGPage(bestslot); - - /* - * 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. - */ - } -} - -/* - * This must be called ONCE during postmaster or standalone-backend startup, - * after StartupXLOG has initialized ShmemVariableCache->nextXid. - */ -void -StartupCLOG(void) -{ - /* - * Initialize our idea of the latest page number. - */ - ClogCtl->latest_page_number = TransactionIdToPage(ShmemVariableCache->nextXid); -} - -/* - * This must be called ONCE during postmaster or standalone-backend shutdown - */ -void -ShutdownCLOG(void) -{ - int slotno; - - LWLockAcquire(CLogControlLock, LW_EXCLUSIVE); - - for (slotno = 0; slotno < NUM_CLOG_BUFFERS; slotno++) - { - WriteCLOGPage(slotno); - Assert(ClogCtl->page_status[slotno] == CLOG_PAGE_EMPTY || - ClogCtl->page_status[slotno] == CLOG_PAGE_CLEAN); - } - - LWLockRelease(CLogControlLock); -} - -/* - * Perform a checkpoint --- either during shutdown, or on-the-fly - */ -void -CheckPointCLOG(void) -{ - int slotno; - - LWLockAcquire(CLogControlLock, LW_EXCLUSIVE); - - for (slotno = 0; slotno < NUM_CLOG_BUFFERS; slotno++) - { - WriteCLOGPage(slotno); - - /* - * We cannot assert that the slot is clean now, since another - * process might have re-dirtied it already. That's okay. - */ - } - - LWLockRelease(CLogControlLock); -} - - -/* - * Make sure that CLOG has room for a newly-allocated XID. - * - * NB: this is called while holding XidGenLock. We want it to be very fast - * most of the time; even when it's not so fast, no actual I/O need happen - * unless we're forced to write out a dirty clog or xlog page to make room - * in shared memory. - */ -void -ExtendCLOG(TransactionId newestXact) -{ - int pageno; - - /* - * No work except at first XID of a page. But beware: just after - * wraparound, the first XID of page zero is FirstNormalTransactionId. - */ - if (TransactionIdToPgIndex(newestXact) != 0 && - !TransactionIdEquals(newestXact, FirstNormalTransactionId)) - return; - - pageno = TransactionIdToPage(newestXact); - - LWLockAcquire(CLogControlLock, LW_EXCLUSIVE); - - /* Zero the page and make an XLOG entry about it */ - ZeroCLOGPage(pageno, true); - - LWLockRelease(CLogControlLock); -} - - -/* - * Remove all CLOG segments before the one holding the passed transaction ID - * - * When this is called, we know that the database logically contains no - * reference to transaction IDs older than oldestXact. However, we must - * not truncate the CLOG until we have performed a checkpoint, to ensure - * that no such references remain on disk either; else a crash just after - * the truncation might leave us with a problem. Since CLOG segments hold - * a large number of transactions, the opportunity to actually remove a - * segment is fairly rare, and so it seems best not to do the checkpoint - * unless we have confirmed that there is a removable segment. Therefore - * we issue the checkpoint command here, not in higher-level code as might - * seem cleaner. - */ -void -TruncateCLOG(TransactionId oldestXact) -{ - int cutoffPage; - int slotno; - - /* - * The cutoff point is the start of the segment containing oldestXact. - */ - oldestXact -= oldestXact % CLOG_XACTS_PER_SEGMENT; - cutoffPage = TransactionIdToPage(oldestXact); - - if (!ScanCLOGDirectory(cutoffPage, false)) - return; /* nothing to remove */ - - /* Perform a CHECKPOINT */ - CreateCheckPoint(false); - - /* - * Scan CLOG shared memory and remove any pages preceding the cutoff - * page, to ensure we won't rewrite them later. (Any dirty pages - * should have been flushed already during the checkpoint, we're just - * being extra careful here.) - */ - LWLockAcquire(CLogControlLock, LW_EXCLUSIVE); - -restart:; - - /* - * While we are holding the lock, make an important safety check: the - * planned cutoff point must be <= the current CLOG endpoint page. - * Otherwise we have already wrapped around, and proceeding with the - * truncation would risk removing the current CLOG segment. - */ - if (CLOGPagePrecedes(ClogCtl->latest_page_number, cutoffPage)) - { - LWLockRelease(CLogControlLock); - elog(LOG, "unable to truncate commit log: apparent wraparound"); - return; - } - - for (slotno = 0; slotno < NUM_CLOG_BUFFERS; slotno++) - { - if (ClogCtl->page_status[slotno] == CLOG_PAGE_EMPTY) - continue; - if (!CLOGPagePrecedes(ClogCtl->page_number[slotno], cutoffPage)) - continue; - - /* - * If page is CLEAN, just change state to EMPTY (expected case). - */ - if (ClogCtl->page_status[slotno] == CLOG_PAGE_CLEAN) - { - ClogCtl->page_status[slotno] = CLOG_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 SelectLRUCLOGPage. - */ - if (ClogCtl->page_status[slotno] == CLOG_PAGE_READ_IN_PROGRESS) - (void) ReadCLOGPage(ClogCtl->page_number[slotno]); - else - WriteCLOGPage(slotno); - goto restart; - } - - LWLockRelease(CLogControlLock); - - /* Now we can remove the old CLOG segment(s) */ - (void) ScanCLOGDirectory(cutoffPage, true); -} - -/* - * TruncateCLOG subroutine: scan CLOG directory for removable segments. - * Actually remove them iff doDeletions is true. Return TRUE iff any - * removable segments were found. Note: no locking is needed. - */ -static bool -ScanCLOGDirectory(int cutoffPage, bool doDeletions) -{ - bool found = false; - DIR *cldir; - struct dirent *clde; - int segno; - int segpage; - char path[MAXPGPATH]; - - cldir = opendir(ClogDir); - if (cldir == NULL) - elog(PANIC, "could not open transaction-commit log directory (%s): %m", - ClogDir); - - errno = 0; - while ((clde = readdir(cldir)) != NULL) - { - if (strlen(clde->d_name) == 4 && - strspn(clde->d_name, "0123456789ABCDEF") == 4) - { - segno = (int) strtol(clde->d_name, NULL, 16); - segpage = segno * CLOG_PAGES_PER_SEGMENT; - if (CLOGPagePrecedes(segpage, cutoffPage)) - { - found = true; - if (doDeletions) - { - elog(LOG, "removing commit log file %s", clde->d_name); - snprintf(path, MAXPGPATH, "%s/%s", ClogDir, clde->d_name); - unlink(path); - } - } - } - errno = 0; - } - if (errno) - elog(PANIC, "could not read transaction-commit log directory (%s): %m", - ClogDir); - closedir(cldir); - - return found; -} - -/* - * Decide which of two CLOG page numbers is "older" for truncation purposes. - * - * We need to use comparison of TransactionIds here in order to do the right - * thing with wraparound XID arithmetic. However, if we are asked about - * page number zero, we don't want to hand InvalidTransactionId to - * TransactionIdPrecedes: it'll get weird about permanent xact IDs. So, - * offset both xids by FirstNormalTransactionId to avoid that. - */ -static bool -CLOGPagePrecedes(int page1, int page2) -{ - TransactionId xid1; - TransactionId xid2; - - xid1 = ((TransactionId) page1) * CLOG_XACTS_PER_PAGE; - xid1 += FirstNormalTransactionId; - xid2 = ((TransactionId) page2) * CLOG_XACTS_PER_PAGE; - xid2 += FirstNormalTransactionId; - - return TransactionIdPrecedes(xid1, xid2); -} - - -/* - * Write a ZEROPAGE xlog record - * - * Note: xlog record is marked as outside transaction control, since we - * want it to be redone whether the invoking transaction commits or not. - * (Besides which, this is normally done just before entering a transaction.) - */ -static void -WriteZeroPageXlogRec(int pageno) -{ - XLogRecData rdata; - - rdata.buffer = InvalidBuffer; - rdata.data = (char *) (&pageno); - rdata.len = sizeof(int); - rdata.next = NULL; - (void) XLogInsert(RM_CLOG_ID, CLOG_ZEROPAGE | XLOG_NO_TRAN, &rdata); -} - -/* - * CLOG resource manager's routines - */ -void -clog_redo(XLogRecPtr lsn, XLogRecord *record) -{ - uint8 info = record->xl_info & ~XLR_INFO_MASK; - - if (info == CLOG_ZEROPAGE) - { - int pageno; - int slotno; - - memcpy(&pageno, XLogRecGetData(record), sizeof(int)); - - LWLockAcquire(CLogControlLock, LW_EXCLUSIVE); - - slotno = ZeroCLOGPage(pageno, false); - WriteCLOGPage(slotno); - Assert(ClogCtl->page_status[slotno] == CLOG_PAGE_CLEAN); - - LWLockRelease(CLogControlLock); - } -} - -void -clog_undo(XLogRecPtr lsn, XLogRecord *record) -{ -} - -void -clog_desc(char *buf, uint8 xl_info, char *rec) -{ - uint8 info = xl_info & ~XLR_INFO_MASK; - - if (info == CLOG_ZEROPAGE) - { - int pageno; - - memcpy(&pageno, rec, sizeof(int)); - sprintf(buf + strlen(buf), "zeropage: %d", pageno); - } - else - strcat(buf, "UNKNOWN"); -} |