Allow BASE_BACKUP to be throttled

A new MAX_RATE option allows imposing a limit to the network transfer
rate from the server side.  This is useful to limit the stress that
taking a base backup has on the server.

pg_basebackup is now able to specify a value to the server, too.

Author: Antonin Houska

Patch reviewed by Stefan Radomski, Andres Freund, Zoltán Böszörményi,
Fujii Masao, and Álvaro Herrera.

Author: alvherre

doc/src/sgml/protocol.sgml

@@ -1772,7 +1772,7 @@ The commands accepted in walsender mode are:
   </varlistentry>
 
   <varlistentry>
-    <term>BASE_BACKUP [<literal>LABEL</literal> <replaceable>'label'</replaceable>] [<literal>PROGRESS</literal>] [<literal>FAST</literal>] [<literal>WAL</literal>] [<literal>NOWAIT</literal>]</term>
+    <term>BASE_BACKUP [<literal>LABEL</literal> <replaceable>'label'</replaceable>] [<literal>PROGRESS</literal>] [<literal>FAST</literal>] [<literal>WAL</literal>] [<literal>NOWAIT</literal>] [<literal>MAX_RATE</literal> <replaceable>rate</replaceable>]</term>
     <listitem>
      <para>
       Instructs the server to start streaming a base backup.
@@ -1840,7 +1840,21 @@ The commands accepted in walsender mode are:
           the waiting and the warning, leaving the client responsible for
           ensuring the required log is available.
          </para>
-         </listitem>
+        </listitem>
+       </varlistentry>
+
+       <varlistentry>
+        <term><literal>MAX_RATE</literal> <replaceable>rate</></term>
+        <listitem>
+         <para>
+          Limit (throttle) the maximum amount of data transferred from server
+          to client per unit of time.  The expected unit is kilobytes per second.
+          If this option is specified, the value must either be equal to zero
+          or it must fall within the range from 32 kB through 1 GB (inclusive).
+          If zero is passed or the option is not specified, no restriction is
+          imposed on the transfer.
+         </para>
+        </listitem>
        </varlistentry>
       </variablelist>
      </para>

doc/src/sgml/ref/pg_basebackup.sgml

@@ -188,6 +188,27 @@ PostgreSQL documentation
       </listitem>
      </varlistentry>
 
+     <varlistentry>
+      <term><option>-r <replaceable class="parameter">rate</replaceable></option></term>
+      <term><option>--max-rate=<replaceable class="parameter">rate</replaceable></option></term>
+      <listitem>
+       <para>
+        The maximum transfer rate of data transferred from the server.  Values are
+        in kilobytes per second.  Use a suffix of <literal>M</> to indicate megabytes
+        per second.  A suffix of <literal>k</> is also accepted, and has no effect.
+        Valid values are between 32 kilobytes per second and 1024 megabytes per second.
+       </para>
+       <para>
+        The purpose is to limit the impact of <application>pg_basebackup</application>
+        on the running server.
+       </para>
+       <para>
+        This option always affects transfer of the data directory. Transfer of
+        WAL files is only affected if the collection method is <literal>fetch</literal>.
+       </para>
+      </listitem>
+     </varlistentry>
+
      <varlistentry>
       <term><option>-R</option></term>
       <term><option>--write-recovery-conf</option></term>

src/backend/replication/basebackup.c

@@ -25,6 +25,7 @@
 #include "libpq/pqformat.h"
 #include "miscadmin.h"
 #include "nodes/pg_list.h"
+#include "pgtar.h"
 #include "pgstat.h"
 #include "replication/basebackup.h"
 #include "replication/walsender.h"
@@ -34,7 +35,8 @@
 #include "utils/builtins.h"
 #include "utils/elog.h"
 #include "utils/ps_status.h"
-#include "pgtar.h"
+#include "utils/timestamp.h"
+
 
 typedef struct
 {
@@ -43,6 +45,7 @@ typedef struct
 	bool		fastcheckpoint;
 	bool		nowait;
 	bool		includewal;
+	uint32		maxrate;
 } basebackup_options;
 
 
@@ -60,6 +63,7 @@ static void perform_base_backup(basebackup_options *opt, DIR *tblspcdir);
 static void parse_basebackup_options(List *options, basebackup_options *opt);
 static void SendXlogRecPtrResult(XLogRecPtr ptr, TimeLineID tli);
 static int	compareWalFileNames(const void *a, const void *b);
+static void throttle(size_t increment);
 
 /* Was the backup currently in-progress initiated in recovery mode? */
 static bool backup_started_in_recovery = false;
@@ -72,6 +76,23 @@ static char *statrelpath = NULL;
  */
 #define TAR_SEND_SIZE 32768
 
+/*
+ * How frequently to throttle, as a fraction of the specified rate-second.
+ */
+#define THROTTLING_FREQUENCY	8
+
+/* The actual number of bytes, transfer of which may cause sleep. */
+static uint64 throttling_sample;
+
+/* Amount of data already transfered but not yet throttled.  */
+static int64 throttling_counter;
+
+/* The minimum time required to transfer throttling_sample bytes. */
+static int64 elapsed_min_unit;
+
+/* The last check of the transfer rate. */
+static int64 throttled_last;
+
 typedef struct
 {
 	char	   *oid;
@@ -203,6 +224,29 @@ perform_base_backup(basebackup_options *opt, DIR *tblspcdir)
 		/* Send tablespace header */
 		SendBackupHeader(tablespaces);
 
+		/* Setup and activate network throttling, if client requested it */
+		if (opt->maxrate > 0)
+		{
+			throttling_sample = opt->maxrate * 1024 / THROTTLING_FREQUENCY;
+
+			/*
+			 * The minimum amount of time for throttling_sample
+			 * bytes to be transfered.
+			 */
+			elapsed_min_unit = USECS_PER_SEC / THROTTLING_FREQUENCY;
+
+			/* Enable throttling. */
+			throttling_counter = 0;
+
+			/* The 'real data' starts now (header was ignored). */
+			throttled_last = GetCurrentIntegerTimestamp();
+		}
+		else
+		{
+			/* Disable throttling. */
+			throttling_counter = -1;
+		}
+
 		/* Send off our tablespaces one by one */
 		foreach(lc, tablespaces)
 		{
@@ -430,6 +474,8 @@ perform_base_backup(basebackup_options *opt, DIR *tblspcdir)
 							(errmsg("base backup could not send data, aborting backup")));
 
 				len += cnt;
+				throttle(cnt);
+
 				if (len == XLogSegSize)
 					break;
 			}
@@ -500,6 +546,7 @@ parse_basebackup_options(List *options, basebackup_options *opt)
 	bool		o_fast = false;
 	bool		o_nowait = false;
 	bool		o_wal = false;
+	bool		o_maxrate = false;
 
 	MemSet(opt, 0, sizeof(*opt));
 	foreach(lopt, options)
@@ -551,6 +598,25 @@ parse_basebackup_options(List *options, basebackup_options *opt)
 			opt->includewal = true;
 			o_wal = true;
 		}
+		else if (strcmp(defel->defname, "max_rate") == 0)
+		{
+			long		maxrate;
+
+			if (o_maxrate)
+				ereport(ERROR,
+						(errcode(ERRCODE_SYNTAX_ERROR),
+						 errmsg("duplicate option \"%s\"", defel->defname)));
+
+			maxrate = intVal(defel->arg);
+			if (maxrate < MAX_RATE_LOWER || maxrate > MAX_RATE_UPPER)
+				ereport(ERROR,
+						(errcode(ERRCODE_NUMERIC_VALUE_OUT_OF_RANGE),
+						 errmsg("%d is outside the valid range for parameter \"%s\" (%d .. %d)",
+								(int) maxrate, "MAX_RATE", MAX_RATE_LOWER, MAX_RATE_UPPER)));
+
+			opt->maxrate = (uint32) maxrate;
+			o_maxrate = true;
+		}
 		else
 			elog(ERROR, "option \"%s\" not recognized",
 				 defel->defname);
@@ -1112,6 +1178,7 @@ sendFile(char *readfilename, char *tarfilename, struct stat * statbuf,
 			   (errmsg("base backup could not send data, aborting backup")));
 
 		len += cnt;
+		throttle(cnt);
 
 		if (len >= statbuf->st_size)
 		{
@@ -1133,10 +1200,14 @@ sendFile(char *readfilename, char *tarfilename, struct stat * statbuf,
 			cnt = Min(sizeof(buf), statbuf->st_size - len);
 			pq_putmessage('d', buf, cnt);
 			len += cnt;
+			throttle(cnt);
 		}
 	}
 
-	/* Pad to 512 byte boundary, per tar format requirements */
+	/*
+	 * Pad to 512 byte boundary, per tar format requirements. (This small
+	 * piece of data is probably not worth throttling.)
+	 */
 	pad = ((len + 511) & ~511) - len;
 	if (pad > 0)
 	{
@@ -1162,3 +1233,65 @@ _tarWriteHeader(const char *filename, const char *linktarget,
 
 	pq_putmessage('d', h, 512);
 }
+
+/*
+ * Increment the network transfer counter by the given number of bytes,
+ * and sleep if necessary to comply with the requested network transfer
+ * rate.
+ */
+static void
+throttle(size_t increment)
+{
+	int64		elapsed,
+				elapsed_min,
+				sleep;
+	int			wait_result;
+
+	if (throttling_counter < 0)
+		return;
+
+	throttling_counter += increment;
+	if (throttling_counter < throttling_sample)
+		return;
+
+	/* Time elapsed since the last measurement (and possible wake up). */
+	elapsed = GetCurrentIntegerTimestamp() - throttled_last;
+	/* How much should have elapsed at minimum? */
+	elapsed_min = elapsed_min_unit * (throttling_counter / throttling_sample);
+	sleep = elapsed_min - elapsed;
+	/* Only sleep if the transfer is faster than it should be. */
+	if (sleep > 0)
+	{
+		ResetLatch(&MyWalSnd->latch);
+
+		/*
+		 * (TAR_SEND_SIZE / throttling_sample * elapsed_min_unit) should be
+		 * the maximum time to sleep. Thus the cast to long is safe.
+		 */
+		wait_result = WaitLatch(&MyWalSnd->latch,
+								WL_LATCH_SET | WL_TIMEOUT | WL_POSTMASTER_DEATH,
+								(long) (sleep / 1000));
+	}
+	else
+	{
+		/*
+		 * The actual transfer rate is below the limit.  A negative value would
+		 * distort the adjustment of throttled_last.
+		 */
+		wait_result = 0;
+		sleep = 0;
+	}
+
+	/*
+	 * Only a whole multiple of throttling_sample was processed. The rest will
+	 * be done during the next call of this function.
+	 */
+	throttling_counter %= throttling_sample;
+
+	/* Once the (possible) sleep has ended, new period starts. */
+	if (wait_result & WL_TIMEOUT)
+		throttled_last += elapsed + sleep;
+	else if (sleep > 0)
+		/* Sleep was necessary but might have been interrupted. */
+		throttled_last = GetCurrentIntegerTimestamp();
+}

src/backend/replication/repl_gram.y

@@ -69,6 +69,7 @@ Node *replication_parse_result;
 %token K_PROGRESS
 %token K_FAST
 %token K_NOWAIT
+%token K_MAX_RATE
 %token K_WAL
 %token K_TIMELINE
 %token K_PHYSICAL
@@ -113,7 +114,7 @@ identify_system:
 			;
 
 /*
- * BASE_BACKUP [LABEL '<label>'] [PROGRESS] [FAST] [WAL] [NOWAIT]
+ * BASE_BACKUP [LABEL '<label>'] [PROGRESS] [FAST] [WAL] [NOWAIT] [MAX_RATE %d]
  */
 base_backup:
 			K_BASE_BACKUP base_backup_opt_list
@@ -157,6 +158,11 @@ base_backup_opt:
 				  $$ = makeDefElem("nowait",
 								   (Node *)makeInteger(TRUE));
 				}
+			| K_MAX_RATE UCONST
+				{
+				  $$ = makeDefElem("max_rate",
+								   (Node *)makeInteger($2));
+				}
 			;
 
 /* CREATE_REPLICATION_SLOT SLOT slot PHYSICAL */

src/backend/replication/repl_scanner.l

@@ -86,6 +86,7 @@ IDENTIFY_SYSTEM		{ return K_IDENTIFY_SYSTEM; }
 LABEL			{ return K_LABEL; }
 NOWAIT			{ return K_NOWAIT; }
 PROGRESS			{ return K_PROGRESS; }
+MAX_RATE		{ return K_MAX_RATE; }
 WAL			{ return K_WAL; }
 TIMELINE			{ return K_TIMELINE; }
 START_REPLICATION	{ return K_START_REPLICATION; }