greenplumn slru 源码
greenplumn slru 代码
文件路径：/src/backend/access/transam/slru.c
/*-------------------------------------------------------------------------
*
* 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) 1996-2019, 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 "pgstat.h"
#include "storage/fd.h"
#include "storage/shmem.h"
#include "miscadmin.h"
#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.
*/
#define MAX_FLUSH_BUFFERS 16
typedef struct SlruFlushData
{
int num_files; /* # files actually open */
int fd[MAX_FLUSH_BUFFERS]; /* their FD's */
int segno[MAX_FLUSH_BUFFERS]; /* their log seg#s */
} SlruFlushData;
typedef struct SlruFlushData *SlruFlush;
/*
* 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, SlruFlush fdata);
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);
static bool SlruScanDirCbDeleteCutoff(SlruCtl ctl, char *filename,
int segpage, void *data);
static void SlruInternalDeleteSegment(SlruCtl ctl, char *filename);
/*
* 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;
}
void
SimpleLruInit(SlruCtl ctl, const char *name, int nslots, int nlsns,
LWLock *ctllock, const char *subdir, int tranche_id)
{
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 */
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));
}
Assert(strlen(name) + 1 < SLRU_MAX_NAME_LENGTH);
strlcpy(shared->lwlock_tranche_name, name, SLRU_MAX_NAME_LENGTH);
shared->lwlock_tranche_id = tranche_id;
ptr += BUFFERALIGN(offset);
for (slotno = 0; slotno < nslots; slotno++)
{
LWLockInitialize(&shared->buffer_locks[slotno].lock,
shared->lwlock_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);
/* Register SLRU tranche in the main tranches array */
LWLockRegisterTranche(shared->lwlock_tranche_id,
shared->lwlock_tranche_name);
/*
* 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_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;
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);
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);
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);
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, SlruFlush 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);
}
/*
* 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;
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))
{
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;
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 = 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;
}
if (lseek(fd, (off_t) offset, SEEK_SET) < 0)
{
slru_errcause = SLRU_SEEK_FAILED;
slru_errno = errno;
CloseTransientFile(fd);
return false;
}
errno = 0;
pgstat_report_wait_start(WAIT_EVENT_SLRU_READ);
if (read(fd, shared->page_buffer[slotno], BLCKSZ) != BLCKSZ)
{
pgstat_report_wait_end();
slru_errcause = SLRU_READ_FAILED;
slru_errno = errno;
CloseTransientFile(fd);
return false;
}
pgstat_report_wait_end();
if (CloseTransientFile(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;
/*
* 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 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.)
*
* 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_FLUSH_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;
}
}
}
if (lseek(fd, (off_t) offset, SEEK_SET) < 0)
{
slru_errcause = SLRU_SEEK_FAILED;
slru_errno = errno;
if (!fdata)
CloseTransientFile(fd);
return false;
}
errno = 0;
pgstat_report_wait_start(WAIT_EVENT_SLRU_WRITE);
if (write(fd, shared->page_buffer[slotno], BLCKSZ) != 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();
/*
* If not part of Flush, need to fsync now. We assume this happens
* infrequently enough that it's not a performance issue.
*/
if (!fdata)
{
pgstat_report_wait_start(WAIT_EVENT_SLRU_SYNC);
if (ctl->do_fsync && pg_fsync(fd))
{
pgstat_report_wait_end();
slru_errcause = SLRU_FSYNC_FAILED;
slru_errno = errno;
CloseTransientFile(fd);
return false;
}
pgstat_report_wait_end();
if (CloseTransientFile(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_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(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.
*/
}
}
/*
* Flush dirty pages to disk during checkpoint or database shutdown
*/
void
SimpleLruFlush(SlruCtl ctl, bool allow_redirtied)
{
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 < 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 fsync and close any files that were open
*/
ok = true;
for (i = 0; i < fdata.num_files; i++)
{
pgstat_report_wait_start(WAIT_EVENT_SLRU_FLUSH_SYNC);
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;
}
pgstat_report_wait_end();
if (CloseTransientFile(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
*/
static void
SimpleLruTruncate_internal(SlruCtl ctl, int cutoffPage, bool lockHeld)
{
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.)
*/
if (!lockHeld)
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))
{
if (!lockHeld)
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? 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;
}
if (!lockHeld)
LWLockRelease(shared->ControlLock);
/* Now we can remove the old segment(s) */
(void) SlruScanDirectory(ctl, SlruScanDirCbDeleteCutoff, &cutoffPage);
}
void
SimpleLruTruncate(SlruCtl ctl, int cutoffPage)
{
SimpleLruTruncate_internal(ctl, cutoffPage, false);
}
/* Like SimpleLruTruncate, but we're already holding the control lock */
void
SimpleLruTruncateWithLock(SlruCtl ctl, int cutoffPage)
{
SimpleLruTruncate_internal(ctl, cutoffPage, true);
}
/*
* Delete an individual SLRU segment, identified by the filename.
*
* 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, char *filename)
{
char path[MAXPGPATH];
snprintf(path, MAXPGPATH, "%s/%s", ctl->Dir, filename);
ereport(DEBUG2,
(errmsg("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;
char path[MAXPGPATH];
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;
snprintf(path, MAXPGPATH, "%s/%04X", ctl->Dir, segno);
ereport(DEBUG2,
(errmsg("removing file \"%s\"", path)));
unlink(path);
LWLockRelease(shared->ControlLock);
}
/*
* SlruScanDirectory callback
* This callback reports true if there's any segment prior to the one
* containing the page passed as "data".
*/
bool
SlruScanDirCbReportPresence(SlruCtl ctl, char *filename, int segpage, void *data)
{
int cutoffPage = *(int *) data;
cutoffPage -= cutoffPage % SLRU_PAGES_PER_SEGMENT;
if (ctl->PagePrecedes(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 (ctl->PagePrecedes(segpage, cutoffPage))
SlruInternalDeleteSegment(ctl, filename);
return false; /* keep going */
}
/*
* SlruScanDirectory callback.
* This callback deletes all segments.
*/
bool
SlruScanDirCbDeleteAll(SlruCtl ctl, char *filename, int segpage, void *data)
{
SlruInternalDeleteSegment(ctl, filename);
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;
}
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