diff options
Diffstat (limited to 'src/backend/access/transam/slru.c')
| -rw-r--r-- | src/backend/access/transam/slru.c | 132 |
1 files changed, 65 insertions, 67 deletions
diff --git a/src/backend/access/transam/slru.c b/src/backend/access/transam/slru.c index 67d9d3f54f3..5891890b764 100644 --- a/src/backend/access/transam/slru.c +++ b/src/backend/access/transam/slru.c @@ -48,7 +48,7 @@ * Portions Copyright (c) 1996-2005, PostgreSQL Global Development Group * Portions Copyright (c) 1994, Regents of the University of California * - * $PostgreSQL: pgsql/src/backend/access/transam/slru.c,v 1.27 2005/08/20 23:26:08 tgl Exp $ + * $PostgreSQL: pgsql/src/backend/access/transam/slru.c,v 1.28 2005/10/15 02:49:09 momjian Exp $ * *------------------------------------------------------------------------- */ @@ -186,8 +186,8 @@ SimpleLruInit(SlruCtl ctl, const char *name, Assert(found); /* - * Initialize the unshared control struct, including directory path. - * We assume caller set PagePrecedes. + * Initialize the unshared control struct, including directory path. We + * assume caller set PagePrecedes. */ ctl->shared = shared; ctl->do_fsync = true; /* default behavior */ @@ -351,11 +351,11 @@ SimpleLruWritePage(SlruCtl ctl, int slotno, SlruFlush fdata) LWLockAcquire(shared->buffer_locks[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. + * 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 (shared->page_number[slotno] != pageno || (shared->page_status[slotno] != SLRU_PAGE_DIRTY && @@ -368,15 +368,14 @@ SimpleLruWritePage(SlruCtl ctl, int slotno, SlruFlush fdata) /* * 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.) + * 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.) */ shared->page_status[slotno] = SLRU_PAGE_WRITE_IN_PROGRESS; @@ -436,8 +435,8 @@ SlruPhysicalReadPage(SlruCtl ctl, int pageno, int slotno) * 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. + * SlruPhysicalWritePage). 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) @@ -528,17 +527,16 @@ SlruPhysicalWritePage(SlruCtl ctl, int pageno, int slotno, SlruFlush fdata) { /* * 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.) + * 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.) */ SlruFileName(ctl, path, segno); fd = BasicOpenFile(path, O_RDWR | PG_BINARY, S_IRUSR | S_IWUSR); @@ -635,49 +633,49 @@ SlruReportIOError(SlruCtl ctl, int pageno, TransactionId xid) case SLRU_OPEN_FAILED: ereport(ERROR, (errcode_for_file_access(), - errmsg("could not access status of transaction %u", xid), + errmsg("could not access status of transaction %u", xid), errdetail("could not open file \"%s\": %m", path))); break; case SLRU_CREATE_FAILED: ereport(ERROR, (errcode_for_file_access(), - errmsg("could not access status of transaction %u", xid), + errmsg("could not access status of transaction %u", xid), errdetail("could not create 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 %u: %m", - path, offset))); + errmsg("could not access status of transaction %u", xid), + errdetail("could not seek in file \"%s\" to offset %u: %m", + path, offset))); break; case SLRU_READ_FAILED: ereport(ERROR, (errcode_for_file_access(), - errmsg("could not access status of transaction %u", xid), - errdetail("could not read from file \"%s\" at offset %u: %m", - path, offset))); + errmsg("could not access status of transaction %u", xid), + errdetail("could not read from file \"%s\" at offset %u: %m", + path, offset))); break; case SLRU_WRITE_FAILED: ereport(ERROR, (errcode_for_file_access(), - errmsg("could not access status of transaction %u", xid), - errdetail("could not write to file \"%s\" at offset %u: %m", - path, offset))); + errmsg("could not access status of transaction %u", xid), + errdetail("could not write to file \"%s\" at offset %u: %m", + path, offset))); break; case SLRU_FSYNC_FAILED: ereport(ERROR, (errcode_for_file_access(), - errmsg("could not access status of transaction %u", xid), + 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), + errmsg("could not access status of transaction %u", xid), errdetail("could not close file \"%s\": %m", path))); break; @@ -723,8 +721,8 @@ SlruSelectLRUPage(SlruCtl ctl, int pageno) } /* - * If we find any EMPTY slot, just select that one. Else locate - * the least-recently-used slot that isn't the latest page. + * If we find any EMPTY slot, just select that one. Else locate the + * least-recently-used slot that isn't the latest page. */ for (slotno = 0; slotno < NUM_SLRU_BUFFERS; slotno++) { @@ -745,10 +743,10 @@ SlruSelectLRUPage(SlruCtl ctl, int pageno) 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 SimpleLruReadPage to wait - * for the read to complete. + * 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 SimpleLruReadPage to wait for the read + * to complete. */ if (shared->page_status[bestslot] == SLRU_PAGE_READ_IN_PROGRESS) (void) SimpleLruReadPage(ctl, shared->page_number[bestslot], @@ -757,9 +755,9 @@ SlruSelectLRUPage(SlruCtl ctl, int pageno) SimpleLruWritePage(ctl, bestslot, 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. + * 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. */ } } @@ -789,9 +787,9 @@ SimpleLruFlush(SlruCtl ctl, bool checkpoint) SimpleLruWritePage(ctl, slotno, &fdata); /* - * When called during a checkpoint, we cannot assert that the slot - * is clean now, since another process might have re-dirtied it - * already. That's okay. + * When called during a checkpoint, we cannot assert that the slot is + * clean now, since another process might have re-dirtied it already. + * That's okay. */ Assert(checkpoint || shared->page_status[slotno] == SLRU_PAGE_EMPTY || @@ -841,10 +839,10 @@ SimpleLruTruncate(SlruCtl ctl, int cutoffPage) cutoffPage -= cutoffPage % SLRU_PAGES_PER_SEGMENT; /* - * 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.) + * 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); @@ -852,16 +850,16 @@ restart:; /* * While we are holding the lock, make an important safety check: the - * planned cutoff point must be <= the current endpoint page. - * Otherwise we have already wrapped around, and proceeding with the - * truncation would risk removing the current segment. + * planned cutoff point must be <= the current endpoint page. Otherwise we + * have already wrapped around, and proceeding with the truncation would + * risk removing the current segment. */ if (ctl->PagePrecedes(shared->latest_page_number, cutoffPage)) { LWLockRelease(shared->ControlLock); ereport(LOG, - (errmsg("could not truncate directory \"%s\": apparent wraparound", - ctl->Dir))); + (errmsg("could not truncate directory \"%s\": apparent wraparound", + ctl->Dir))); return; } @@ -882,9 +880,9 @@ restart:; } /* - * 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. + * 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. */ if (shared->page_status[slotno] == SLRU_PAGE_READ_IN_PROGRESS) (void) SimpleLruReadPage(ctl, shared->page_number[slotno], |