(reviving an old thread)
On 08/24/2013 12:53 AM, Josh Berkus wrote:
On 08/23/2013 02:08 PM, Heikki Linnakangas wrote:
Here's a bigger patch, which does more. It is based on the ideas in the
post I started this thread with, with feedback incorporated from the
long discussion. With this patch, WAL disk space usage is controlled by
two GUCs:
min_recycle_wal_size
checkpoint_wal_size
<snip>
These settings are fairly intuitive for a DBA to tune. You begin by
figuring out how much disk space you can afford to spend on WAL, and set
checkpoint_wal_size to that (with some safety margin, of course). Then
you set checkpoint_timeout based on how long you're willing to wait for
recovery to finish. Finally, if you have infrequent batch jobs that need
a lot more WAL than the system otherwise needs, you can set
min_recycle_wal_size to keep enough WAL preallocated for the spikes.
We'll want to rename them to make it even *more* intuitive.
Sure, I'm all ears.
But ... do I understand things correctly that checkpoint wouldn't "kick
in" until you hit checkpoint_wal_size? If that's the case, isn't real
disk space usage around 2X checkpoint_wal_size if spread checkpoint is
set to 0.9? Or does checkpoint kick in sometime earlier?
It kicks in earlier, so that the checkpoint *completes* just when
checkpoint_wal_size of WAL is used up. So the real disk usage is
checkpoint_wal_size.
There is still an internal variable called CheckPointSegments that
triggers the checkpoint, but it is now derived from checkpoint_wal_size
(see CalculateCheckpointSegments function):
CheckPointSegments = (checkpoint_wal_size / 16 MB) / (2 +
checkpoint_completion_target)
This is the same formula we've always had in the manual for calculating
the amount of WAL space used, but in reverse. I.e. we calculate
CheckPointSegments based on the desired disk space usage, not the other
way round.
As a note, pgBench would be a terrible test for this patch; we really
need something which creates uneven traffic. I'll see if I can devise
something.
Attached is a rebased version of this patch. Everyone, please try this
out on whatever workloads you have, and let me know:
a) How does the auto-tuning of the number of recycled segments work?
Does pg_xlog reach a steady-state size, or does it fluctuate a lot?
b) Are the two GUCs, checkpoint_wal_size, and min_recycle_wal_size,
intuitive to set?
- Heikki
diff --git a/doc/src/sgml/config.sgml b/doc/src/sgml/config.sgml
index 6bcb106..34f9466 100644
--- a/doc/src/sgml/config.sgml
+++ b/doc/src/sgml/config.sgml
@@ -1325,7 +1325,7 @@ include_dir 'conf.d'
40% of RAM to <varname>shared_buffers</varname> will work better than a
smaller amount. Larger settings for <varname>shared_buffers</varname>
usually require a corresponding increase in
- <varname>checkpoint_segments</varname>, in order to spread out the
+ <varname>checkpoint_wal_size</varname>, in order to spread out the
process of writing large quantities of new or changed data over a
longer period of time.
</para>
@@ -2394,18 +2394,21 @@ include_dir 'conf.d'
<title>Checkpoints</title>
<variablelist>
- <varlistentry id="guc-checkpoint-segments" xreflabel="checkpoint_segments">
- <term><varname>checkpoint_segments</varname> (<type>integer</type>)
+ <varlistentry id="guc-checkpoint-wal-size" xreflabel="checkpoint_wal_size">
+ <term><varname>checkpoint_wal_size</varname> (<type>integer</type>)</term>
<indexterm>
- <primary><varname>checkpoint_segments</> configuration parameter</primary>
+ <primary><varname>checkpoint_wal_size</> configuration parameter</primary>
</indexterm>
</term>
<listitem>
<para>
- Maximum number of log file segments between automatic WAL
- checkpoints (each segment is normally 16 megabytes). The default
- is three segments. Increasing this parameter can increase the
- amount of time needed for crash recovery.
+ Maximum size to let the WAL grow to between automatic WAL
+ checkpoints. This is a soft limit; WAL size can exceed
+ <varname>checkpoint_wal_size</> under special circumstances, like
+ under heavy load, a failing <varname>archive_command</>, or a high
+ <varname>wal_keep_segments</> setting. The default is 128 MB.
+ Increasing this parameter can increase the amount of time needed for
+ crash recovery.
This parameter can only be set in the <filename>postgresql.conf</>
file or on the server command line.
</para>
@@ -2458,7 +2461,7 @@ include_dir 'conf.d'
Write a message to the server log if checkpoints caused by
the filling of checkpoint segment files happen closer together
than this many seconds (which suggests that
- <varname>checkpoint_segments</> ought to be raised). The default is
+ <varname>checkpoint_wal_size</> ought to be raised). The default is
30 seconds (<literal>30s</>). Zero disables the warning.
No warnings will be generated if <varname>checkpoint_timeout</varname>
is less than <varname>checkpoint_warning</varname>.
@@ -2468,6 +2471,24 @@ include_dir 'conf.d'
</listitem>
</varlistentry>
+ <varlistentry id="guc-min-recycle-wal-size" xreflabel="min_recycle_wal_size">
+ <term><varname>min_recycle_wal_size</varname> (<type>integer</type>)</term>
+ <indexterm>
+ <primary><varname>min_recycle_wal_size</> configuration parameter</primary>
+ </indexterm>
+ <listitem>
+ <para>
+ As long as WAL disk usage stays below this setting, old WAL files are
+ always recycled for future use at a checkpoint, rather than removed.
+ This can be used to ensure that enough WAL space is reserved to
+ handle spikes in WAL usage, for example when running large batch
+ jobs. The default is 80 MB.
+ This parameter can only be set in the <filename>postgresql.conf</>
+ file or on the server command line.
+ </para>
+ </listitem>
+ </varlistentry>
+
</variablelist>
</sect2>
<sect2 id="runtime-config-wal-archiving">
diff --git a/doc/src/sgml/perform.sgml b/doc/src/sgml/perform.sgml
index 5a087fb..24022d9 100644
--- a/doc/src/sgml/perform.sgml
+++ b/doc/src/sgml/perform.sgml
@@ -1328,19 +1328,19 @@ SELECT * FROM x, y, a, b, c WHERE something AND somethingelse;
</para>
</sect2>
- <sect2 id="populate-checkpoint-segments">
- <title>Increase <varname>checkpoint_segments</varname></title>
+ <sect2 id="populate-checkpoint-wal-size">
+ <title>Increase <varname>checkpoint_wal_size</varname></title>
<para>
Temporarily increasing the <xref
- linkend="guc-checkpoint-segments"> configuration variable can also
+ linkend="guc-checkpoint-wal-size"> configuration variable can also
make large data loads faster. This is because loading a large
amount of data into <productname>PostgreSQL</productname> will
cause checkpoints to occur more often than the normal checkpoint
frequency (specified by the <varname>checkpoint_timeout</varname>
configuration variable). Whenever a checkpoint occurs, all dirty
pages must be flushed to disk. By increasing
- <varname>checkpoint_segments</varname> temporarily during bulk
+ <varname>checkpoint-wal-size</varname> temporarily during bulk
data loads, the number of checkpoints that are required can be
reduced.
</para>
@@ -1445,7 +1445,7 @@ SELECT * FROM x, y, a, b, c WHERE something AND somethingelse;
<para>
Set appropriate (i.e., larger than normal) values for
<varname>maintenance_work_mem</varname> and
- <varname>checkpoint_segments</varname>.
+ <varname>checkpoint_wal_size</varname>.
</para>
</listitem>
<listitem>
@@ -1512,7 +1512,7 @@ SELECT * FROM x, y, a, b, c WHERE something AND somethingelse;
So when loading a data-only dump, it is up to you to drop and recreate
indexes and foreign keys if you wish to use those techniques.
- It's still useful to increase <varname>checkpoint_segments</varname>
+ It's still useful to increase <varname>checkpoint_wal_size</varname>
while loading the data, but don't bother increasing
<varname>maintenance_work_mem</varname>; rather, you'd do that while
manually recreating indexes and foreign keys afterwards.
@@ -1577,7 +1577,7 @@ SELECT * FROM x, y, a, b, c WHERE something AND somethingelse;
<listitem>
<para>
- Increase <xref linkend="guc-checkpoint-segments"> and <xref
+ Increase <xref linkend="guc-checkpoint-wal-size"> and <xref
linkend="guc-checkpoint-timeout"> ; this reduces the frequency
of checkpoints, but increases the storage requirements of
<filename>/pg_xlog</>.
diff --git a/doc/src/sgml/wal.sgml b/doc/src/sgml/wal.sgml
index 1254c03..6cf7772 100644
--- a/doc/src/sgml/wal.sgml
+++ b/doc/src/sgml/wal.sgml
@@ -472,9 +472,10 @@
<para>
The server's checkpointer process automatically performs
a checkpoint every so often. A checkpoint is begun every <xref
- linkend="guc-checkpoint-segments"> log segments, or every <xref
- linkend="guc-checkpoint-timeout"> seconds, whichever comes first.
- The default settings are 3 segments and 300 seconds (5 minutes), respectively.
+ linkend="guc-checkpoint-timeout"> seconds, or if
+ <xref linkend="guc-checkpoint-wal-size"> is about to be exceeded, whichever
+ comes first.
+ The default settings are 5 minutes and 128 MB, respectively.
If no WAL has been written since the previous checkpoint, new checkpoints
will be skipped even if <varname>checkpoint_timeout</> has passed.
(If WAL archiving is being used and you want to put a lower limit on how
@@ -486,8 +487,8 @@
</para>
<para>
- Reducing <varname>checkpoint_segments</varname> and/or
- <varname>checkpoint_timeout</varname> causes checkpoints to occur
+ Reducing <varname>checkpoint_timeout</varname> and/or
+ <varname>checkpoint_wal_size</varname> causes checkpoints to occur
more often. This allows faster after-crash recovery, since less work
will need to be redone. However, one must balance this against the
increased cost of flushing dirty data pages more often. If
@@ -510,11 +511,11 @@
parameter. If checkpoints happen closer together than
<varname>checkpoint_warning</> seconds,
a message will be output to the server log recommending increasing
- <varname>checkpoint_segments</varname>. Occasional appearance of such
+ <varname>checkpoint_wal_size</varname>. Occasional appearance of such
a message is not cause for alarm, but if it appears often then the
checkpoint control parameters should be increased. Bulk operations such
as large <command>COPY</> transfers might cause a number of such warnings
- to appear if you have not set <varname>checkpoint_segments</> high
+ to appear if you have not set <varname>checkpoint_wal_size</> high
enough.
</para>
@@ -525,10 +526,10 @@
<xref linkend="guc-checkpoint-completion-target">, which is
given as a fraction of the checkpoint interval.
The I/O rate is adjusted so that the checkpoint finishes when the
- given fraction of <varname>checkpoint_segments</varname> WAL segments
- have been consumed since checkpoint start, or the given fraction of
- <varname>checkpoint_timeout</varname> seconds have elapsed,
- whichever is sooner. With the default value of 0.5,
+ given fraction of
+ <varname>checkpoint_timeout</varname> seconds have elapsed, or before
+ <varname>checkpoint_wal_size</varname> is exceeded, whichever is sooner.
+ With the default value of 0.5,
<productname>PostgreSQL</> can be expected to complete each checkpoint
in about half the time before the next checkpoint starts. On a system
that's very close to maximum I/O throughput during normal operation,
@@ -545,18 +546,33 @@
</para>
<para>
- There will always be at least one WAL segment file, and will normally
- not be more than (2 + <varname>checkpoint_completion_target</varname>) * <varname>checkpoint_segments</varname> + 1
- or <varname>checkpoint_segments</> + <xref linkend="guc-wal-keep-segments"> + 1
- files. Each segment file is normally 16 MB (though this size can be
- altered when building the server). You can use this to estimate space
- requirements for <acronym>WAL</acronym>.
- Ordinarily, when old log segment files are no longer needed, they
- are recycled (that is, renamed to become future segments in the numbered
- sequence). If, due to a short-term peak of log output rate, there
- are more than 3 * <varname>checkpoint_segments</varname> + 1
- segment files, the unneeded segment files will be deleted instead
- of recycled until the system gets back under this limit.
+ The number of WAL segment files in <filename>pg_xlog</> directory depends on
+ <varname>checkpoint_wal_size</>, <varname>wal_recycle_min_size</> and the
+ amount of WAL generated in previous checkpoint cycles. When old log
+ segment files are no longer needed, they are removed or recycled (that is,
+ renamed to become future segments in the numbered sequence). If, due to a
+ short-term peak of log output rate, <varname>checkpoint_wal_size</> is
+ exceeded, the unneeded segment files will be removed until the system
+ gets back under this limit. Below that limit, the system recycles enough
+ WAL files to cover the estimated need until the next checkpoint, and
+ removes the rest. The estimate is based on a moving average of the number
+ of WAL files used in previous checkpoint cycles. The moving average
+ is increased immediately if the actual usage exceeds the estimate, so it
+ accommodates peak usage rather average usage to some extent.
+ <varname>wal_recycle_min_size</> puts a minimum on the amount of WAL files
+ recycled for future usage; that much WAL is always recycled for future use,
+ even if the system is idle and the WAL usage estimate suggests that little
+ WAL is needed.
+ </para>
+
+ <para>
+ Independently of <varname>checkpoint_wal_size</varname>,
+ <xref linkend="guc-wal-keep-segments"> + 1 most recent WAL files are
+ kept at all times. Also, if WAL archiving is used, old segments can not be
+ removed or recycled until they are archived. If WAL archiving cannot keep up
+ with the pace that WAL is generated, or if <varname>archive_command</varname>
+ fails repeatedly, old WAL files will accumulate in <filename>pg_xlog</>
+ until the situation is resolved.
</para>
<para>
@@ -571,9 +587,8 @@
master because restartpoints can only be performed at checkpoint records.
A restartpoint is triggered when a checkpoint record is reached if at
least <varname>checkpoint_timeout</> seconds have passed since the last
- restartpoint. In standby mode, a restartpoint is also triggered if at
- least <varname>checkpoint_segments</> log segments have been replayed
- since the last restartpoint.
+ restartpoint, or if WAL size is about to exceed
+ <varname>checkpoint_wal_size</>.
</para>
<para>
diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c
index e5dddd4..07aa92b 100644
--- a/src/backend/access/transam/xlog.c
+++ b/src/backend/access/transam/xlog.c
@@ -79,7 +79,8 @@ extern uint32 bootstrap_data_checksum_version;
/* User-settable parameters */
-int CheckPointSegments = 3;
+int checkpoint_wal_size = 131072; /* 128 MB */
+int min_recycle_wal_size = 81920; /* 80 MB */
int wal_keep_segments = 0;
int XLOGbuffers = -1;
int XLogArchiveTimeout = 0;
@@ -106,18 +107,14 @@ bool XLOG_DEBUG = false;
#define NUM_XLOGINSERT_LOCKS 8
/*
- * XLOGfileslop is the maximum number of preallocated future XLOG segments.
- * When we are done with an old XLOG segment file, we will recycle it as a
- * future XLOG segment as long as there aren't already XLOGfileslop future
- * segments; else we'll delete it. This could be made a separate GUC
- * variable, but at present I think it's sufficient to hardwire it as
- * 2*CheckPointSegments+1. Under normal conditions, a checkpoint will free
- * no more than 2*CheckPointSegments log segments, and we want to recycle all
- * of them; the +1 allows boundary cases to happen without wasting a
- * delete/create-segment cycle.
+ * Max distance from last checkpoint, before triggering a new xlog-based
+ * checkpoint.
*/
-#define XLOGfileslop (2*CheckPointSegments + 1)
+int CheckPointSegments;
+/* Estimated distance between checkpoints, in bytes */
+static double CheckPointDistanceEstimate = 0;
+static double PrevCheckPointDistance = 0;
/*
* GUC support
@@ -778,7 +775,7 @@ static void AdvanceXLInsertBuffer(XLogRecPtr upto, bool opportunistic);
static bool XLogCheckpointNeeded(XLogSegNo new_segno);
static void XLogWrite(XLogwrtRqst WriteRqst, bool flexible);
static bool InstallXLogFileSegment(XLogSegNo *segno, char *tmppath,
- bool find_free, int *max_advance,
+ bool find_free, XLogSegNo max_segno,
bool use_lock);
static int XLogFileRead(XLogSegNo segno, int emode, TimeLineID tli,
int source, bool notexistOk);
@@ -791,7 +788,7 @@ static bool WaitForWALToBecomeAvailable(XLogRecPtr RecPtr, bool randAccess,
static int emode_for_corrupt_record(int emode, XLogRecPtr RecPtr);
static void XLogFileClose(void);
static void PreallocXlogFiles(XLogRecPtr endptr);
-static void RemoveOldXlogFiles(XLogSegNo segno, XLogRecPtr endptr);
+static void RemoveOldXlogFiles(XLogSegNo segno, XLogRecPtr PriorRedoPtr, XLogRecPtr endptr);
static void UpdateLastRemovedPtr(char *filename);
static void ValidateXLOGDirectoryStructure(void);
static void CleanupBackupHistory(void);
@@ -1958,6 +1955,109 @@ AdvanceXLInsertBuffer(XLogRecPtr upto, bool opportunistic)
}
/*
+ * Calculate CheckPointSegments based on checkpoint_wal_size and
+ * checkpoint_completion_target.
+ */
+static void
+CalculateCheckpointSegments(void)
+{
+ double target;
+
+ /*-------
+ * Calculate the distance at which to trigger a checkpoint, to avoid
+ * exceeding checkpoint_wal_size. This is based on two assumptions:
+ *
+ * a) we keep WAL for two checkpoint cycles, back to the "prev" checkpoint.
+ * b) during checkpoint, we consume checkpoint_completion_target *
+ * number of segments consumed between checkpoints.
+ *-------
+ */
+ target = (double ) checkpoint_wal_size / (double) (XLOG_SEG_SIZE / 1024);
+ target = target / (2.0 + CheckPointCompletionTarget);
+
+ /* round down */
+ CheckPointSegments = (int) target;
+
+ if (CheckPointSegments < 1)
+ CheckPointSegments = 1;
+}
+
+void
+assign_checkpoint_wal_size(int newval, void *extra)
+{
+ checkpoint_wal_size = newval;
+ CalculateCheckpointSegments();
+}
+
+void
+assign_checkpoint_completion_target(double newval, void *extra)
+{
+ CheckPointCompletionTarget = newval;
+ CalculateCheckpointSegments();
+}
+
+/*
+ * At a checkpoint, how many WAL segments to recycle as preallocated future
+ * XLOG segments? Returns the highest segment that should be preallocated.
+ */
+static XLogSegNo
+XLOGfileslop(XLogRecPtr PriorRedoPtr)
+{
+ double nsegments;
+ XLogSegNo minSegNo;
+ XLogSegNo maxSegNo;
+ double distance;
+ XLogSegNo recycleSegNo;
+
+ /*
+ * Calculate the segment numbers that min_recycle_wal_size and
+ * checkpoint_wal_size correspond to. Always recycle enough segments
+ * to meet the minimum, and remove enough segments to stay below the
+ * maximum.
+ */
+ nsegments = (double) min_recycle_wal_size / (double) (XLOG_SEG_SIZE / 1024);
+ minSegNo = PriorRedoPtr / XLOG_SEG_SIZE + (int) nsegments - 1;
+ nsegments = (double) checkpoint_wal_size / (double) (XLOG_SEG_SIZE / 1024);
+ maxSegNo = PriorRedoPtr / XLOG_SEG_SIZE + (int) nsegments - 1;
+
+ /*
+ * Between those limits, recycle enough segments to get us through to the
+ * estimated end of next checkpoint.
+ *
+ * To estimate where the next checkpoint will finish, assume that the
+ * system runs steadily consuming CheckPointDistanceEstimate
+ * bytes between every checkpoint.
+ *
+ * The reason this calculation is done from the prior checkpoint, not the
+ * one that just finished, is that this behaves better if some checkpoint
+ * cycles are abnormally short, like if you perform a manual checkpoint
+ * right after a timed one. The manual checkpoint will make almost a full
+ * cycle's worth of WAL segments available for recycling, because the
+ * segments from the prior's prior, fully-sized checkpoint cycle are no
+ * longer needed. However, the next checkpoint will make only few segments
+ * available for recycling, the ones generated between the timed
+ * checkpoint and the manual one right after that. If at the manual
+ * checkpoint we only retained enough segments to get us to the next timed
+ * one, and removed the rest, then at the next checkpoint we would not
+ * have enough segments around for recycling, to get us to the checkpoint
+ * after that. Basing the calculations on the distance from the prior redo
+ * pointer largely fixes that problem.
+ */
+ distance = (2.0 + CheckPointCompletionTarget) * CheckPointDistanceEstimate;
+ /* add 10% for good measure. */
+ distance *= 1.10;
+
+ recycleSegNo = (XLogSegNo) ceil(((double) PriorRedoPtr + distance) / XLOG_SEG_SIZE);
+
+ if (recycleSegNo < minSegNo)
+ recycleSegNo = minSegNo;
+ if (recycleSegNo > maxSegNo)
+ recycleSegNo = maxSegNo;
+
+ return recycleSegNo;
+}
+
+/*
* Check whether we've consumed enough xlog space that a checkpoint is needed.
*
* new_segno indicates a log file that has just been filled up (or read
@@ -2764,7 +2864,7 @@ XLogFileInit(XLogSegNo logsegno, bool *use_existent, bool use_lock)
char zbuffer_raw[XLOG_BLCKSZ + MAXIMUM_ALIGNOF];
char *zbuffer;
XLogSegNo installed_segno;
- int max_advance;
+ XLogSegNo max_segno;
int fd;
int nbytes;
@@ -2867,9 +2967,19 @@ XLogFileInit(XLogSegNo logsegno, bool *use_existent, bool use_lock)
* pre-create a future log segment.
*/
installed_segno = logsegno;
- max_advance = XLOGfileslop;
+
+ /*
+ * XXX: What should we use as max_segno? We used to use XLOGfileslop when
+ * that was a constant, but that was always a bit dubious: normally, at a
+ * checkpoint, XLOGfileslop was the offset from the checkpoint record,
+ * but here, it was the offset from the insert location. We can't do the
+ * normal XLOGfileslop calculation here because we don't have access to
+ * the prior checkpoint's redo location. So somewhat arbitrarily, just
+ * use CheckPointSegments.
+ */
+ max_segno = logsegno + CheckPointSegments;
if (!InstallXLogFileSegment(&installed_segno, tmppath,
- *use_existent, &max_advance,
+ *use_existent, max_segno,
use_lock))
{
/*
@@ -3010,7 +3120,7 @@ XLogFileCopy(XLogSegNo destsegno, TimeLineID srcTLI, XLogSegNo srcsegno,
/*
* Now move the segment into place with its final name.
*/
- if (!InstallXLogFileSegment(&destsegno, tmppath, false, NULL, false))
+ if (!InstallXLogFileSegment(&destsegno, tmppath, false, 0, false))
elog(ERROR, "InstallXLogFileSegment should not have failed");
}
@@ -3030,22 +3140,21 @@ XLogFileCopy(XLogSegNo destsegno, TimeLineID srcTLI, XLogSegNo srcsegno,
* number at or after the passed numbers. If FALSE, install the new segment
* exactly where specified, deleting any existing segment file there.
*
- * *max_advance: maximum number of segno slots to advance past the starting
- * point. Fail if no free slot is found in this range. On return, reduced
- * by the number of slots skipped over. (Irrelevant, and may be NULL,
- * when find_free is FALSE.)
+ * max_segno: maximum segment number to install the new file as. Fail if no
+ * free slot is found between *segno and max_segno. (Ignored when find_free
+ * is FALSE.)
*
* use_lock: if TRUE, acquire ControlFileLock while moving file into
* place. This should be TRUE except during bootstrap log creation. The
* caller must *not* hold the lock at call.
*
* Returns TRUE if the file was installed successfully. FALSE indicates that
- * max_advance limit was exceeded, or an error occurred while renaming the
+ * max_segno limit was exceeded, or an error occurred while renaming the
* file into place.
*/
static bool
InstallXLogFileSegment(XLogSegNo *segno, char *tmppath,
- bool find_free, int *max_advance,
+ bool find_free, XLogSegNo max_segno,
bool use_lock)
{
char path[MAXPGPATH];
@@ -3069,7 +3178,7 @@ InstallXLogFileSegment(XLogSegNo *segno, char *tmppath,
/* Find a free slot to put it in */
while (stat(path, &stat_buf) == 0)
{
- if (*max_advance <= 0)
+ if ((*segno) >= max_segno)
{
/* Failed to find a free slot within specified range */
if (use_lock)
@@ -3077,7 +3186,6 @@ InstallXLogFileSegment(XLogSegNo *segno, char *tmppath,
return false;
}
(*segno)++;
- (*max_advance)--;
XLogFilePath(path, ThisTimeLineID, *segno);
}
}
@@ -3425,14 +3533,15 @@ UpdateLastRemovedPtr(char *filename)
/*
* Recycle or remove all log files older or equal to passed segno
*
- * endptr is current (or recent) end of xlog; this is used to determine
+ * endptr is current (or recent) end of xlog, and PriorRedoRecPtr is the
+ * redo pointer of the previous checkpoint. These are used to determine
* whether we want to recycle rather than delete no-longer-wanted log files.
*/
static void
-RemoveOldXlogFiles(XLogSegNo segno, XLogRecPtr endptr)
+RemoveOldXlogFiles(XLogSegNo segno, XLogRecPtr PriorRedoPtr, XLogRecPtr endptr)
{
XLogSegNo endlogSegNo;
- int max_advance;
+ XLogSegNo recycleSegNo;
DIR *xldir;
struct dirent *xlde;
char lastoff[MAXFNAMELEN];
@@ -3444,11 +3553,10 @@ RemoveOldXlogFiles(XLogSegNo segno, XLogRecPtr endptr)
struct stat statbuf;
/*
- * Initialize info about where to try to recycle to. We allow recycling
- * segments up to XLOGfileslop segments beyond the current XLOG location.
+ * Initialize info about where to try to recycle to.
*/
XLByteToPrevSeg(endptr, endlogSegNo);
- max_advance = XLOGfileslop;
+ recycleSegNo = XLOGfileslop(PriorRedoPtr);
xldir = AllocateDir(XLOGDIR);
if (xldir == NULL)
@@ -3497,20 +3605,17 @@ RemoveOldXlogFiles(XLogSegNo segno, XLogRecPtr endptr)
* for example can create symbolic links pointing to a
* separate archive directory.
*/
- if (lstat(path, &statbuf) == 0 && S_ISREG(statbuf.st_mode) &&
+ if (endlogSegNo <= recycleSegNo &&
+ lstat(path, &statbuf) == 0 && S_ISREG(statbuf.st_mode) &&
InstallXLogFileSegment(&endlogSegNo, path,
- true, &max_advance, true))
+ true, recycleSegNo, true))
{
ereport(DEBUG2,
(errmsg("recycled transaction log file \"%s\"",
xlde->d_name)));
CheckpointStats.ckpt_segs_recycled++;
/* Needn't recheck that slot on future iterations */
- if (max_advance > 0)
- {
- endlogSegNo++;
- max_advance--;
- }
+ endlogSegNo++;
}
else
{
@@ -7598,7 +7703,8 @@ LogCheckpointEnd(bool restartpoint)
elog(LOG, "%s complete: wrote %d buffers (%.1f%%); "
"%d transaction log file(s) added, %d removed, %d recycled; "
"write=%ld.%03d s, sync=%ld.%03d s, total=%ld.%03d s; "
- "sync files=%d, longest=%ld.%03d s, average=%ld.%03d s",
+ "sync files=%d, longest=%ld.%03d s, average=%ld.%03d s; "
+ "distance=%d KB, estimate=%d KB",
restartpoint ? "restartpoint" : "checkpoint",
CheckpointStats.ckpt_bufs_written,
(double) CheckpointStats.ckpt_bufs_written * 100 / NBuffers,
@@ -7610,7 +7716,48 @@ LogCheckpointEnd(bool restartpoint)
total_secs, total_usecs / 1000,
CheckpointStats.ckpt_sync_rels,
longest_secs, longest_usecs / 1000,
- average_secs, average_usecs / 1000);
+ average_secs, average_usecs / 1000,
+ (int) (PrevCheckPointDistance / 1024.0),
+ (int) (CheckPointDistanceEstimate / 1024.0));
+}
+
+/*
+ * Update the estimate of distance between checkpoints.
+ *
+ * The estimate is used to calculate the number of WAL segments to keep
+ * preallocated, see XLOGFileSlop().
+ */
+static void
+UpdateCheckPointDistanceEstimate(uint64 nbytes)
+{
+ /*
+ * To estimate the number of segments consumed between checkpoints, keep
+ * a moving average of the actual number of segments consumed in previous
+ * checkpoint cycles. However, if the load is bursty, with quiet periods
+ * and busy periods, we want to cater for the peak load. So instead of a
+ * plain moving average, let the average decline slowly if the previous
+ * cycle used less WAL than estimated, but bump it up immediately if it
+ * used more.
+ *
+ * When checkpoints are triggered by checkpoint_wal_size, this should
+ * converge to CheckpointSegments * XLOG_SEG_SIZE,
+ *
+ * Note: This doesn't pay any attention to what caused the checkpoint.
+ * Checkpoints triggered manually with CHECKPOINT command, or by e.g
+ * starting a base backup, are counted the same as those created
+ * automatically. The slow-decline will largely mask them out, if they are
+ * not frequent. If they are frequent, it seems reasonable to count them
+ * in as any others; if you issue a manual checkpoint every 5 minutes and
+ * never let a timed checkpoint happen, it makes sense to base the
+ * preallocation on that 5 minute interval rather than whatever
+ * checkpoint_timeout is set to.
+ */
+ PrevCheckPointDistance = nbytes;
+ if (CheckPointDistanceEstimate < nbytes)
+ CheckPointDistanceEstimate = nbytes;
+ else
+ CheckPointDistanceEstimate =
+ (0.90 * CheckPointDistanceEstimate + 0.10 * (double) nbytes);
}
/*
@@ -7650,7 +7797,7 @@ CreateCheckPoint(int flags)
XLogRecPtr recptr;
XLogCtlInsert *Insert = &XLogCtl->Insert;
uint32 freespace;
- XLogSegNo _logSegNo;
+ XLogRecPtr PriorRedoPtr;
XLogRecPtr curInsert;
VirtualTransactionId *vxids;
int nvxids;
@@ -7965,10 +8112,10 @@ CreateCheckPoint(int flags)
(errmsg("concurrent transaction log activity while database system is shutting down")));
/*
- * Select point at which we can truncate the log, which we base on the
- * prior checkpoint's earliest info.
+ * Remember the prior checkpoint's redo pointer, used later to determine
+ * the point where the log can be truncated.
*/
- XLByteToSeg(ControlFile->checkPointCopy.redo, _logSegNo);
+ PriorRedoPtr = ControlFile->checkPointCopy.redo;
/*
* Update the control file.
@@ -8023,11 +8170,17 @@ CreateCheckPoint(int flags)
* Delete old log files (those no longer needed even for previous
* checkpoint or the standbys in XLOG streaming).
*/
- if (_logSegNo)
+ if (PriorRedoPtr != InvalidXLogRecPtr)
{
+ XLogSegNo _logSegNo;
+
+ /* Update the average distance between checkpoints. */
+ UpdateCheckPointDistanceEstimate(RedoRecPtr - PriorRedoPtr);
+
+ XLByteToSeg(PriorRedoPtr, _logSegNo);
KeepLogSeg(recptr, &_logSegNo);
_logSegNo--;
- RemoveOldXlogFiles(_logSegNo, recptr);
+ RemoveOldXlogFiles(_logSegNo, PriorRedoPtr, recptr);
}
/*
@@ -8195,7 +8348,7 @@ CreateRestartPoint(int flags)
{
XLogRecPtr lastCheckPointRecPtr;
CheckPoint lastCheckPoint;
- XLogSegNo _logSegNo;
+ XLogRecPtr PriorRedoPtr;
TimestampTz xtime;
/*
@@ -8260,7 +8413,7 @@ CreateRestartPoint(int flags)
/*
* Update the shared RedoRecPtr so that the startup process can calculate
* the number of segments replayed since last restartpoint, and request a
- * restartpoint if it exceeds checkpoint_segments.
+ * restartpoint if it exceeds CheckPointSegments.
*
* Like in CreateCheckPoint(), hold off insertions to update it, although
* during recovery this is just pro forma, because no WAL insertions are
@@ -8291,10 +8444,10 @@ CreateRestartPoint(int flags)
CheckPointGuts(lastCheckPoint.redo, flags);
/*
- * Select point at which we can truncate the xlog, which we base on the
- * prior checkpoint's earliest info.
+ * Remember the prior checkpoint's redo pointer, used later to determine
+ * the point at which we can truncate the log.
*/
- XLByteToSeg(ControlFile->checkPointCopy.redo, _logSegNo);
+ PriorRedoPtr = ControlFile->checkPointCopy.redo;
/*
* Update pg_control, using current time. Check that it still shows
@@ -8321,12 +8474,15 @@ CreateRestartPoint(int flags)
* checkpoint/restartpoint) to prevent the disk holding the xlog from
* growing full.
*/
- if (_logSegNo)
+ if (PriorRedoPtr != InvalidXLogRecPtr)
{
XLogRecPtr receivePtr;
XLogRecPtr replayPtr;
TimeLineID replayTLI;
XLogRecPtr endptr;
+ XLogSegNo _logSegNo;
+
+ XLByteToSeg(PriorRedoPtr, _logSegNo);
/*
* Get the current end of xlog replayed or received, whichever is
@@ -8355,7 +8511,7 @@ CreateRestartPoint(int flags)
if (RecoveryInProgress())
ThisTimeLineID = replayTLI;
- RemoveOldXlogFiles(_logSegNo, endptr);
+ RemoveOldXlogFiles(_logSegNo, PriorRedoPtr, endptr);
/*
* Make more log segments if needed. (Do this after recycling old log
diff --git a/src/backend/postmaster/checkpointer.c b/src/backend/postmaster/checkpointer.c
index 8a79d9b..1183793 100644
--- a/src/backend/postmaster/checkpointer.c
+++ b/src/backend/postmaster/checkpointer.c
@@ -482,7 +482,7 @@ CheckpointerMain(void)
"checkpoints are occurring too frequently (%d seconds apart)",
elapsed_secs,
elapsed_secs),
- errhint("Consider increasing the configuration parameter \"checkpoint_segments\".")));
+ errhint("Consider increasing the configuration parameter \"checkpoint_wal_size\".")));
/*
* Initialize checkpointer-private variables used during
@@ -760,11 +760,11 @@ IsCheckpointOnSchedule(double progress)
return false;
/*
- * Check progress against WAL segments written and checkpoint_segments.
+ * Check progress against WAL segments written and CheckPointSegments.
*
* We compare the current WAL insert location against the location
* computed before calling CreateCheckPoint. The code in XLogInsert that
- * actually triggers a checkpoint when checkpoint_segments is exceeded
+ * actually triggers a checkpoint when CheckPointSegments is exceeded
* compares against RedoRecptr, so this is not completely accurate.
* However, it's good enough for our purposes, we're only calculating an
* estimate anyway.
diff --git a/src/backend/utils/misc/guc.c b/src/backend/utils/misc/guc.c
index 77c3494..a2aad83 100644
--- a/src/backend/utils/misc/guc.c
+++ b/src/backend/utils/misc/guc.c
@@ -2086,16 +2086,28 @@ static struct config_int ConfigureNamesInt[] =
},
{
- {"checkpoint_segments", PGC_SIGHUP, WAL_CHECKPOINTS,
- gettext_noop("Sets the maximum distance in log segments between automatic WAL checkpoints."),
- NULL
+ {"min_recycle_wal_size", PGC_SIGHUP, WAL_CHECKPOINTS,
+ gettext_noop("Sets the minimum size to shrink the WAL to."),
+ NULL,
+ GUC_UNIT_KB
},
- &CheckPointSegments,
- 3, 1, INT_MAX,
+ &min_recycle_wal_size,
+ 81920, 32768, INT_MAX,
NULL, NULL, NULL
},
{
+ {"checkpoint_wal_size", PGC_SIGHUP, WAL_CHECKPOINTS,
+ gettext_noop("Sets the maximum WAL size that triggers a checkpoint."),
+ NULL,
+ GUC_UNIT_KB
+ },
+ &checkpoint_wal_size,
+ 131072, 32768, INT_MAX,
+ NULL, assign_checkpoint_wal_size, NULL
+ },
+
+ {
{"checkpoint_timeout", PGC_SIGHUP, WAL_CHECKPOINTS,
gettext_noop("Sets the maximum time between automatic WAL checkpoints."),
NULL,
@@ -2711,7 +2723,7 @@ static struct config_real ConfigureNamesReal[] =
},
&CheckPointCompletionTarget,
0.5, 0.0, 1.0,
- NULL, NULL, NULL
+ NULL, assign_checkpoint_completion_target, NULL
},
/* End-of-list marker */
diff --git a/src/backend/utils/misc/postgresql.conf.sample b/src/backend/utils/misc/postgresql.conf.sample
index b053659..fc276a8 100644
--- a/src/backend/utils/misc/postgresql.conf.sample
+++ b/src/backend/utils/misc/postgresql.conf.sample
@@ -197,8 +197,9 @@
# - Checkpoints -
-#checkpoint_segments = 3 # in logfile segments, min 1, 16MB each
#checkpoint_timeout = 5min # range 30s-1h
+#checkpoint_wal_size = 128MB
+#min_recycle_wal_size = 80MB
#checkpoint_completion_target = 0.5 # checkpoint target duration, 0.0 - 1.0
#checkpoint_warning = 30s # 0 disables
diff --git a/src/include/access/xlog.h b/src/include/access/xlog.h
index d06fbc0..d15b8f1 100644
--- a/src/include/access/xlog.h
+++ b/src/include/access/xlog.h
@@ -89,7 +89,8 @@ extern XLogRecPtr XactLastRecEnd;
extern bool reachedConsistency;
/* these variables are GUC parameters related to XLOG */
-extern int CheckPointSegments;
+extern int min_recycle_wal_size;
+extern int checkpoint_wal_size;
extern int wal_keep_segments;
extern int XLOGbuffers;
extern int XLogArchiveTimeout;
@@ -100,6 +101,8 @@ extern bool fullPageWrites;
extern bool wal_log_hints;
extern bool log_checkpoints;
+extern int CheckPointSegments;
+
/* WAL levels */
typedef enum WalLevel
{
@@ -245,6 +248,9 @@ extern bool CheckPromoteSignal(void);
extern void WakeupRecovery(void);
extern void SetWalWriterSleeping(bool sleeping);
+extern void assign_checkpoint_wal_size(int newval, void *extra);
+extern void assign_checkpoint_completion_target(double newval, void *extra);
+
/*
* Starting/stopping a base backup
*/
--
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