/*
* 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 < shared->num_slots; 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_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++)
{
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);
}
/*
* DistributedLog resource manager's routines
*/
void
DistributedLog_redo(XLogRecPtr beginLoc, XLogRecPtr lsn, XLogRecord *record)
{
MIRRORED_LOCK_DECLARE;
uint8 info = record->xl_info & ~XLR_INFO_MASK;
MIRRORED_LOCK;
if (info == DISTRIBUTEDLOG_ZEROPAGE)
{
int page;
int slotno;
memcpy(&page, XLogRecGetData(record), sizeof(int));
elog((Debug_print_full_dtm ? LOG : DEBUG5),
"Redo DISTRIBUTEDLOG_ZEROPAGE page %d",
page);
LWLockAcquire(DistributedLogControlLock, LW_EXCLUSIVE);
slotno = DistributedLog_ZeroPage(page, false);
SimpleLruWritePage(DistributedLogCtl, slotno, NULL);
Assert(!DistributedLogCtl->shared->page_dirty[slotno]);
LWLockRelease(DistributedLogControlLock);
elog((Debug_print_full_dtm ? LOG : DEBUG5),
"DistributedLog_redo zero page = %d",
page);
}
else if (info == DISTRIBUTEDLOG_TRUNCATE)
{
int page;
memcpy(&page, XLogRecGetData(record), sizeof(int));
elog((Debug_print_full_dtm ? LOG : DEBUG5),
"Redo DISTRIBUTEDLOG_TRUNCATE page %d",
page);
/*
* During XLOG replay, latest_page_number isn't set up yet; insert
* a suitable value to bypass the sanity test in SimpleLruTruncate.
*/
DistributedLogCtl->shared->latest_page_number = page;
SimpleLruTruncate(DistributedLogCtl, page);
elog((Debug_print_full_dtm ? LOG : DEBUG5),
"DistributedLog_redo truncate to cutoff page = %d",
page);
}
else
elog(PANIC, "DistributedLog_redo: unknown op code %u", info);
MIRRORED_UNLOCK;
}
/*
* Activate this module whenever necessary.
* This must happen during postmaster or standalong-backend startup,
* or during WAL replay anytime the track_commit_timestamp setting is
* changed in the master.
*
* The reason why this SLRU needs separate activation/deactivation functions is
* that it can be enabled/disabled during start and the activation/deactivation
* on master is propagated to slave via replay. Other SLRUs don't have this
* property and they can be just initialized during normal startup.
*
* This is in charge of creating the currently active segment, if it's not
* already there. The reason for this is that the server might have been
* running with this module disabled for a while and thus might have skipped
* the normal creation point.
*/
static void
ActivateCommitTs(void)
{
TransactionId xid = ShmemVariableCache->nextXid;
int pageno = TransactionIdToCTsPage(xid);
/*
* Re-Initialize our idea of the latest page number.
*/
LWLockAcquire(CommitTsControlLock, LW_EXCLUSIVE);
CommitTsCtl->shared->latest_page_number = pageno;
LWLockRelease(CommitTsControlLock);
/*
* If CommitTs is enabled, but it wasn't in the previous server run, we
* need to set the oldest and newest values to the next Xid; that way, we
* will not try to read data that might not have been set.
*
* XXX does this have a problem if a server is started with commitTs
* enabled, then started with commitTs disabled, then restarted with it
* enabled again? It doesn't look like it does, because there should be a
* checkpoint that sets the value to InvalidTransactionId at end of
* recovery; and so any chance of injecting new transactions without
* CommitTs values would occur after the oldestCommitTs has been set to
* Invalid temporarily.
*/
LWLockAcquire(CommitTsLock, LW_EXCLUSIVE);
if (ShmemVariableCache->oldestCommitTs == InvalidTransactionId)
{
ShmemVariableCache->oldestCommitTs =
ShmemVariableCache->newestCommitTs = ReadNewTransactionId();
}
LWLockRelease(CommitTsLock);
/* Create the current segment file, if necessary */
if (!SimpleLruDoesPhysicalPageExist(CommitTsCtl, pageno))
{
int slotno;
LWLockAcquire(CommitTsControlLock, LW_EXCLUSIVE);
slotno = ZeroCommitTsPage(pageno, false);
SimpleLruWritePage(CommitTsCtl, slotno);
Assert(!CommitTsCtl->shared->page_dirty[slotno]);
LWLockRelease(CommitTsControlLock);
}
/* Change the activation status in shared memory. */
LWLockAcquire(CommitTsLock, LW_EXCLUSIVE);
commitTsShared->commitTsActive = true;
LWLockRelease(CommitTsLock);
}
/*
* This func must be called ONCE on system install. It creates
* the initial SUBTRANS segment. (The SUBTRANS directory is assumed to
* have been created by the initdb shell script, and SUBTRANSShmemInit
* must have been called already.)
*
* Note: it's not really necessary to create the initial segment now,
* since slru.c would create it on first write anyway. But we may as well
* do it to be sure the directory is set up correctly.
*/
void
BootStrapSUBTRANS(void)
{
int slotno;
LWLockAcquire(SubtransControlLock, LW_EXCLUSIVE);
/* Create and zero the first page of the subtrans log */
slotno = ZeroSUBTRANSPage(0);
/* Make sure it's written out */
SimpleLruWritePage(SubTransCtl, slotno);
Assert(!SubTransCtl->shared->page_dirty[slotno]);
LWLockRelease(SubtransControlLock);
}
/*
* This func must be called ONCE on system install. It creates
* the initial DistributedLog segment. (The pg_distributedlog directory is
* assumed to have been created by the initdb shell script, and
* DistributedLog_ShmemInit must have been called already.)
*/
void
DistributedLog_BootStrap(void)
{
MIRRORED_LOCK_DECLARE;
int slotno;
MIRRORED_LOCK;
LWLockAcquire(DistributedLogControlLock, LW_EXCLUSIVE);
/* Create and zero the first page of the commit log */
slotno = DistributedLog_ZeroPage(0, false);
/* Make sure it's written out */
SimpleLruWritePage(DistributedLogCtl, slotno, NULL);
Assert(!DistributedLogCtl->shared->page_dirty[slotno]);
LWLockRelease(DistributedLogControlLock);
MIRRORED_UNLOCK;
}
/*
* CommitTS resource manager's routines
*/
void
commit_ts_redo(XLogReaderState *record)
{
uint8 info = XLogRecGetInfo(record) & ~XLR_INFO_MASK;
/* Backup blocks are not used in commit_ts records */
Assert(!XLogRecHasAnyBlockRefs(record));
if (info == COMMIT_TS_ZEROPAGE)
{
int pageno;
int slotno;
memcpy(&pageno, XLogRecGetData(record), sizeof(int));
LWLockAcquire(CommitTsControlLock, LW_EXCLUSIVE);
slotno = ZeroCommitTsPage(pageno, false);
SimpleLruWritePage(CommitTsCtl, slotno);
Assert(!CommitTsCtl->shared->page_dirty[slotno]);
LWLockRelease(CommitTsControlLock);
}
else if (info == COMMIT_TS_TRUNCATE)
{
int pageno;
memcpy(&pageno, XLogRecGetData(record), sizeof(int));
/*
* During XLOG replay, latest_page_number isn't set up yet; insert a
* suitable value to bypass the sanity test in SimpleLruTruncate.
*/
CommitTsCtl->shared->latest_page_number = pageno;
SimpleLruTruncate(CommitTsCtl, pageno);
}
else if (info == COMMIT_TS_SETTS)
{
xl_commit_ts_set *setts = (xl_commit_ts_set *) XLogRecGetData(record);
int nsubxids;
TransactionId *subxids;
nsubxids = ((XLogRecGetDataLen(record) - SizeOfCommitTsSet) /
sizeof(TransactionId));
if (nsubxids > 0)
{
subxids = palloc(sizeof(TransactionId) * nsubxids);
memcpy(subxids,
XLogRecGetData(record) + SizeOfCommitTsSet,
sizeof(TransactionId) * nsubxids);
}
else
subxids = NULL;
TransactionTreeSetCommitTsData(setts->mainxid, nsubxids, subxids,
setts->timestamp, setts->nodeid, true);
if (subxids)
pfree(subxids);
}
else
elog(PANIC, "commit_ts_redo: unknown op code %u", info);
}
/*
* 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 bestslot;
int best_delta;
int best_page_number;
/* 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 locate the
* least-recently-used slot to replace.
*
* 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.
*
* In no case will we select the slot containing latest_page_number
* for replacement, even if it appears least recently used.
*
* 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)++;
best_delta = -1;
bestslot = 0; /* no-op, just keeps compiler quiet */
best_page_number = 0; /* ditto */
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_delta > best_delta ||
(this_delta == best_delta &&
ctl->PagePrecedes(this_page_number, best_page_number))) &&
this_page_number != shared->latest_page_number)
{
bestslot = slotno;
best_delta = this_delta;
best_page_number = this_page_number;
}
}
/*
* If the selected page is clean, we're set.
*/
if (shared->page_status[bestslot] == SLRU_PAGE_VALID &&
!shared->page_dirty[bestslot])
return bestslot;
/*
* We need to wait for I/O. Normal case is that it's dirty and we
* must initiate a write, but it's possible that the page is already
* write-busy, or in the worst case still read-busy. In those cases
* we wait for the existing I/O to complete.
*/
if (shared->page_status[bestslot] == SLRU_PAGE_VALID)
SimpleLruWritePage(ctl, bestslot, NULL);
else
SimpleLruWaitIO(ctl, 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.
*/
}
}
/*
* 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 < 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)
SimpleLruWritePage(ctl, slotno, NULL);
else
SimpleLruWaitIO(ctl, slotno);
goto restart;
}
LWLockRelease(shared->ControlLock);
/* Now we can remove the old segment(s) */
(void) SlruScanDirectory(ctl, cutoffPage, true);
}
/*
* 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 just wait for someone else to complete the
* I/O, which we can do by waiting for the per-buffer lock.
*/
if (shared->page_status[bestslot] == SLRU_PAGE_READ_IN_PROGRESS)
{
LWLockRelease(shared->ControlLock);
LWLockAcquire(shared->buffer_locks[bestslot], LW_SHARED);
LWLockRelease(shared->buffer_locks[bestslot]);
LWLockAcquire(shared->ControlLock, LW_EXCLUSIVE);
}
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.
*/
}
}
