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/*-------------------------------------------------------------------------
*
* 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. 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.
*
*
* 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 1.26 2005/07/04 04:51:44 tgl Exp $
*
*-------------------------------------------------------------------------
*/
#include "postgres.h"
#include <fcntl.h>
#include <sys/stat.h>
#include <unistd.h>
#include "access/slru.h"
#include "access/xlog.h"
#include "storage/fd.h"
#include "storage/shmem.h"
#include "miscadmin.h"
/*
* Define segment size. A page is the same BLCKSZ as is used everywhere
* else in Postgres. The segment size can be chosen somewhat arbitrarily;
* we make it 32 pages by default, or 256Kb, i.e. 1M transactions for CLOG
* or 64K transactions for SUBTRANS.
*
* Note: because TransactionIds are 32 bits and wrap around at 0xFFFFFFFF,
* page numbering also wraps around at 0xFFFFFFFF/xxxx_XACTS_PER_PAGE (where
* xxxx is CLOG or SUBTRANS, respectively), and segment numbering at
* 0xFFFFFFFF/xxxx_XACTS_PER_PAGE/SLRU_PAGES_PER_SEGMENT. We need
* take no explicit notice of that fact in this module, except when comparing
* segment and page numbers in SimpleLruTruncate (see PagePrecedes()).
*
* Note: this file currently assumes that segment file names will be four
* hex digits. This sets a lower bound on the segment size (64K transactions
* for 32-bit TransactionIds).
*/
#define SLRU_PAGES_PER_SEGMENT 32
#define SlruFileName(ctl, path, seg) \
snprintf(path, MAXPGPATH, "%s/%04X", (ctl)->Dir, seg)
/*
* During SimpleLruFlush(), we will usually not need to write/fsync 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 SimpleLruFlush(). This data structure remembers
* which files are open.
*/
typedef struct SlruFlushData
{
int num_files; /* # files actually open */
int fd[NUM_SLRU_BUFFERS]; /* their FD's */
int segno[NUM_SLRU_BUFFERS]; /* their log seg#s */
} SlruFlushData;
/*
* Macro to mark a buffer slot "most recently used".
*/
#define SlruRecentlyUsed(shared, slotno) \
do { \
if ((shared)->page_lru_count[slotno] != 0) { \
int iilru; \
for (iilru = 0; iilru < NUM_SLRU_BUFFERS; iilru++) \
(shared)->page_lru_count[iilru]++; \
(shared)->page_lru_count[slotno] = 0; \
} \
} while (0)
/* Saved info for SlruReportIOError */
typedef enum
{
SLRU_OPEN_FAILED,
SLRU_CREATE_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 bool SlruPhysicalReadPage(SlruCtl ctl, int pageno, int slotno);
static bool SlruPhysicalWritePage(SlruCtl ctl, int pageno, int slotno,
SlruFlush fdata);
static void SlruReportIOError(SlruCtl ctl, int pageno, TransactionId xid);
static int SlruSelectLRUPage(SlruCtl ctl, int pageno);
/*
* Initialization of shared memory
*/
int
SimpleLruShmemSize(void)
{
return BUFFERALIGN(sizeof(SlruSharedData)) + BLCKSZ * NUM_SLRU_BUFFERS;
}
void
SimpleLruInit(SlruCtl ctl, const char *name,
LWLockId ctllock, const char *subdir)
{
SlruShared shared;
bool found;
shared = (SlruShared) ShmemInitStruct(name, SimpleLruShmemSize(), &found);
if (!IsUnderPostmaster)
{
/* Initialize locks and shared memory area */
char *bufptr;
int slotno;
Assert(!found);
memset(shared, 0, sizeof(SlruSharedData));
shared->ControlLock = ctllock;
bufptr = (char *) shared + BUFFERALIGN(sizeof(SlruSharedData));
for (slotno = 0; slotno < NUM_SLRU_BUFFERS; slotno++)
{
shared->page_buffer[slotno] = bufptr;
shared->page_status[slotno] = SLRU_PAGE_EMPTY;
shared->page_lru_count[slotno] = 1;
shared->buffer_locks[slotno] = LWLockAssign();
bufptr += BLCKSZ;
}
/* shared->latest_page_number will be set later */
}
else
Assert(found);
/*
* Initialize the unshared control struct, including directory path.
* We assume caller set PagePrecedes.
*/
ctl->shared = shared;
ctl->do_fsync = true; /* default behavior */
StrNCpy(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_CLEAN ||
shared->page_number[slotno] == pageno);
/* Mark the slot as containing this page */
shared->page_number[slotno] = pageno;
shared->page_status[slotno] = SLRU_PAGE_DIRTY;
SlruRecentlyUsed(shared, slotno);
/* Set the buffer to zeroes */
MemSet(shared->page_buffer[slotno], 0, BLCKSZ);
/* Assume this page is now the latest active page */
shared->latest_page_number = pageno;
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 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, TransactionId xid)
{
SlruShared shared = ctl->shared;
/* Outer loop handles restart if we lose the buffer to someone else */
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 cannot use it yet */
if (shared->page_status[slotno] != SLRU_PAGE_READ_IN_PROGRESS)
{
/* otherwise, it's ready to use */
SlruRecentlyUsed(shared, slotno);
return slotno;
}
}
else
{
/* We found no match; assert we selected a freeable slot */
Assert(shared->page_status[slotno] == SLRU_PAGE_EMPTY ||
shared->page_status[slotno] == SLRU_PAGE_CLEAN);
}
/* Mark the slot read-busy (no-op if it already was) */
shared->page_number[slotno] = pageno;
shared->page_status[slotno] = SLRU_PAGE_READ_IN_PROGRESS;
/*
* Temporarily mark page as recently-used to discourage
* SlruSelectLRUPage from selecting it again for someone else.
*/
SlruRecentlyUsed(shared, slotno);
/* Release shared lock, grab per-buffer lock instead */
LWLockRelease(shared->ControlLock);
LWLockAcquire(shared->buffer_locks[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 (shared->page_number[slotno] != pageno ||
shared->page_status[slotno] != SLRU_PAGE_READ_IN_PROGRESS)
{
LWLockRelease(shared->buffer_locks[slotno]);
LWLockAcquire(shared->ControlLock, LW_EXCLUSIVE);
continue;
}
/* Okay, do the read */
ok = SlruPhysicalReadPage(ctl, pageno, slotno);
/* Re-acquire shared 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_status[slotno] = ok ? SLRU_PAGE_CLEAN : SLRU_PAGE_EMPTY;
LWLockRelease(shared->buffer_locks[slotno]);
/* Now it's okay to ereport if we failed */
if (!ok)
SlruReportIOError(ctl, pageno, xid);
SlruRecentlyUsed(shared, slotno);
return slotno;
}
}
/*
* 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.
*/
void
SimpleLruWritePage(SlruCtl ctl, int slotno, SlruFlush fdata)
{
SlruShared shared = ctl->shared;
int pageno;
bool ok;
/* Do nothing if page does not need writing */
if (shared->page_status[slotno] != SLRU_PAGE_DIRTY &&
shared->page_status[slotno] != SLRU_PAGE_WRITE_IN_PROGRESS)
return;
pageno = shared->page_number[slotno];
/* Release shared lock, grab per-buffer lock instead */
LWLockRelease(shared->ControlLock);
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.
*/
if (shared->page_number[slotno] != pageno ||
(shared->page_status[slotno] != SLRU_PAGE_DIRTY &&
shared->page_status[slotno] != SLRU_PAGE_WRITE_IN_PROGRESS))
{
LWLockRelease(shared->buffer_locks[slotno]);
LWLockAcquire(shared->ControlLock, 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.)
*/
shared->page_status[slotno] = SLRU_PAGE_WRITE_IN_PROGRESS;
/* Okay, 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++)
close(fdata->fd[i]);
}
/* Re-acquire shared 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 ||
shared->page_status[slotno] == SLRU_PAGE_DIRTY));
/* Cannot set CLEAN if someone re-dirtied page since write started */
if (shared->page_status[slotno] == SLRU_PAGE_WRITE_IN_PROGRESS)
shared->page_status[slotno] = ok ? SLRU_PAGE_CLEAN : SLRU_PAGE_DIRTY;
LWLockRelease(shared->buffer_locks[slotno]);
/* Now it's okay to ereport if we failed */
if (!ok)
SlruReportIOError(ctl, pageno, InvalidTransactionId);
}
/*
* 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;
int 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 = BasicOpenFile(path, O_RDWR | PG_BINARY, S_IRUSR | S_IWUSR);
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;
}
if (lseek(fd, (off_t) offset, SEEK_SET) < 0)
{
slru_errcause = SLRU_SEEK_FAILED;
slru_errno = errno;
close(fd);
return false;
}
errno = 0;
if (read(fd, shared->page_buffer[slotno], BLCKSZ) != BLCKSZ)
{
slru_errcause = SLRU_READ_FAILED;
slru_errno = errno;
close(fd);
return false;
}
if (close(fd))
{
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
* SimpleLruFlush, though.
*
* fdata is NULL for a standalone write, pointer to open-file info during
* SimpleLruFlush.
*/
static bool
SlruPhysicalWritePage(SlruCtl ctl, int pageno, int slotno, SlruFlush fdata)
{
SlruShared shared = ctl->shared;
int segno = pageno / SLRU_PAGES_PER_SEGMENT;
int rpageno = pageno % SLRU_PAGES_PER_SEGMENT;
int offset = rpageno * BLCKSZ;
char path[MAXPGPATH];
int fd = -1;
/*
* During a Flush, 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.)
*/
SlruFileName(ctl, path, segno);
fd = BasicOpenFile(path, O_RDWR | PG_BINARY, S_IRUSR | S_IWUSR);
if (fd < 0)
{
if (errno != ENOENT)
{
slru_errcause = SLRU_OPEN_FAILED;
slru_errno = errno;
return false;
}
fd = BasicOpenFile(path, O_RDWR | O_CREAT | O_EXCL | PG_BINARY,
S_IRUSR | S_IWUSR);
if (fd < 0)
{
slru_errcause = SLRU_CREATE_FAILED;
slru_errno = errno;
return false;
}
}
if (fdata)
{
fdata->fd[fdata->num_files] = fd;
fdata->segno[fdata->num_files] = segno;
fdata->num_files++;
}
}
if (lseek(fd, (off_t) offset, SEEK_SET) < 0)
{
slru_errcause = SLRU_SEEK_FAILED;
slru_errno = errno;
if (!fdata)
close(fd);
return false;
}
errno = 0;
if (write(fd, shared->page_buffer[slotno], BLCKSZ) != BLCKSZ)
{
/* 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)
close(fd);
return false;
}
/*
* If not part of Flush, need to fsync now. We assume this happens
* infrequently enough that it's not a performance issue.
*/
if (!fdata)
{
if (ctl->do_fsync && pg_fsync(fd))
{
slru_errcause = SLRU_FSYNC_FAILED;
slru_errno = errno;
close(fd);
return false;
}
if (close(fd))
{
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_CREATE_FAILED:
ereport(ERROR,
(errcode_for_file_access(),
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)));
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)));
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)));
break;
case SLRU_FSYNC_FAILED:
ereport(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 bestslot = 0;
unsigned int bestcount = 0;
/* See if page already has a buffer assigned */
for (slotno = 0; slotno < NUM_SLRU_BUFFERS; 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 locate
* the least-recently-used slot that isn't the latest page.
*/
for (slotno = 0; slotno < NUM_SLRU_BUFFERS; slotno++)
{
if (shared->page_status[slotno] == SLRU_PAGE_EMPTY)
return slotno;
if (shared->page_lru_count[slotno] > bestcount &&
shared->page_number[slotno] != shared->latest_page_number)
{
bestslot = slotno;
bestcount = shared->page_lru_count[slotno];
}
}
/*
* If the selected page is clean, we're set.
*/
if (shared->page_status[bestslot] == SLRU_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 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],
InvalidTransactionId);
else
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.
*/
}
}
/*
* Flush dirty pages to disk during checkpoint or database shutdown
*/
void
SimpleLruFlush(SlruCtl ctl, bool checkpoint)
{
SlruShared shared = ctl->shared;
SlruFlushData fdata;
int slotno;
int pageno = 0;
int i;
bool ok;
/*
* Find and write dirty pages
*/
fdata.num_files = 0;
LWLockAcquire(shared->ControlLock, LW_EXCLUSIVE);
for (slotno = 0; slotno < NUM_SLRU_BUFFERS; slotno++)
{
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.
*/
Assert(checkpoint ||
shared->page_status[slotno] == SLRU_PAGE_EMPTY ||
shared->page_status[slotno] == SLRU_PAGE_CLEAN);
}
LWLockRelease(shared->ControlLock);
/*
* Now fsync and close any files that were open
*/
ok = true;
for (i = 0; i < fdata.num_files; i++)
{
if (ctl->do_fsync && pg_fsync(fdata.fd[i]))
{
slru_errcause = SLRU_FSYNC_FAILED;
slru_errno = errno;
pageno = fdata.segno[i] * SLRU_PAGES_PER_SEGMENT;
ok = false;
}
if (close(fdata.fd[i]))
{
slru_errcause = SLRU_CLOSE_FAILED;
slru_errno = errno;
pageno = fdata.segno[i] * SLRU_PAGES_PER_SEGMENT;
ok = false;
}
}
if (!ok)
SlruReportIOError(ctl, pageno, InvalidTransactionId);
}
/*
* Remove all segments before the one holding the passed page number
*/
void
SimpleLruTruncate(SlruCtl ctl, int cutoffPage)
{
SlruShared shared = ctl->shared;
int slotno;
/*
* The cutoff point is the start of the segment containing 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.)
*/
LWLockAcquire(shared->ControlLock, LW_EXCLUSIVE);
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.
*/
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 < NUM_SLRU_BUFFERS; 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_CLEAN)
{
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.
*/
if (shared->page_status[slotno] == SLRU_PAGE_READ_IN_PROGRESS)
(void) SimpleLruReadPage(ctl, shared->page_number[slotno],
InvalidTransactionId);
else
SimpleLruWritePage(ctl, slotno, NULL);
goto restart;
}
LWLockRelease(shared->ControlLock);
/* Now we can remove the old segment(s) */
(void) SlruScanDirectory(ctl, cutoffPage, true);
}
/*
* SimpleLruTruncate subroutine: scan directory for removable segments.
* Actually remove them iff doDeletions is true. Return TRUE iff any
* removable segments were found. Note: no locking is needed.
*
* This can be called directly from clog.c, for reasons explained there.
*/
bool
SlruScanDirectory(SlruCtl ctl, int cutoffPage, bool doDeletions)
{
bool found = false;
DIR *cldir;
struct dirent *clde;
int segno;
int segpage;
char path[MAXPGPATH];
/*
* The cutoff point is the start of the segment containing cutoffPage.
* (This is redundant when called from SimpleLruTruncate, but not when
* called directly from clog.c.)
*/
cutoffPage -= cutoffPage % SLRU_PAGES_PER_SEGMENT;
cldir = AllocateDir(ctl->Dir);
while ((clde = ReadDir(cldir, ctl->Dir)) != NULL)
{
if (strlen(clde->d_name) == 4 &&
strspn(clde->d_name, "0123456789ABCDEF") == 4)
{
segno = (int) strtol(clde->d_name, NULL, 16);
segpage = segno * SLRU_PAGES_PER_SEGMENT;
if (ctl->PagePrecedes(segpage, cutoffPage))
{
found = true;
if (doDeletions)
{
snprintf(path, MAXPGPATH, "%s/%s", ctl->Dir, clde->d_name);
ereport(DEBUG2,
(errmsg("removing file \"%s\"", path)));
unlink(path);
}
}
}
}
FreeDir(cldir);
return found;
}