On Sat, Jan 7, 2017 at 7:48 PM, Jim Nasby <jim.na...@bluetreble.com> wrote:
> On 1/5/17 12:55 PM, Jonathon Nelson wrote:
>
>> Attached please find a patch for PostgreSQL 9.4 which changes the
>> maximum amount of data that the wal sender will send at any point in
>> time from the hard-coded value of 128KiB to a user-controllable value up
>> to 16MiB. It has been primarily tested under 9.4 but there has been some
>> testing with 9.5.
>>
>
> To make sure this doesn't get lost, please add it to
> https://commitfest.postgresql.org. Please verify the patch will apply
> against current HEAD and pass make check-world.
Attached please find a revision of the patch, changed in the following ways:
1. removed a call to debug2.
2. applies cleanly against master (as of 8c5722948e831c1862a39da2bb5d79
3a6f2aabab)
3. one small indentation fix, one small verbiage fix.
4. switched to calculating the upper bound using XLOG_SEG_SIZE rather than
hard-coding 16384.
5. the git author is - obviously - different.
make check-world passes.
I have added it to the commitfest.
I have verified with strace that up to 16MB sends are being used.
I have verified that the GUC properly grumps about values greater than
XLOG_SEG_SIZE / 1024 or smaller than 4.
--
Jon
From 7286e290daec32e12260e9e1e44a490c13ed2245 Mon Sep 17 00:00:00 2001
From: Jon Nelson <jnel...@jamponi.net>
Date: Mon, 9 Jan 2017 20:00:41 -0600
Subject: [PATCH] guc-ify the formerly hard-coded MAX_SEND_SIZE to max_wal_send
---
src/backend/replication/walsender.c | 13 +++++++------
src/backend/utils/misc/guc.c | 12 ++++++++++++
2 files changed, 19 insertions(+), 6 deletions(-)
diff --git a/src/backend/replication/walsender.c b/src/backend/replication/walsender.c
index f3082c3..4a9eb16 100644
--- a/src/backend/replication/walsender.c
+++ b/src/backend/replication/walsender.c
@@ -91,7 +91,7 @@
* because signals are checked only between messages. 128kB (with
* default 8k blocks) seems like a reasonable guess for now.
*/
-#define MAX_SEND_SIZE (XLOG_BLCKSZ * 16)
+int max_wal_send_guc = 0;
/* Array of WalSnds in shared memory */
WalSndCtlData *WalSndCtl = NULL;
@@ -2194,7 +2194,7 @@ retry:
/*
* Send out the WAL in its normal physical/stored form.
*
- * Read up to MAX_SEND_SIZE bytes of WAL that's been flushed to disk,
+ * Read up to max_wal_send kilobytes of WAL that's been flushed to disk,
* but not yet sent to the client, and buffer it in the libpq output
* buffer.
*
@@ -2208,6 +2208,7 @@ XLogSendPhysical(void)
XLogRecPtr startptr;
XLogRecPtr endptr;
Size nbytes;
+ int max_wal_send = max_wal_send_guc * 1024;
if (streamingDoneSending)
{
@@ -2346,8 +2347,8 @@ XLogSendPhysical(void)
/*
* Figure out how much to send in one message. If there's no more than
- * MAX_SEND_SIZE bytes to send, send everything. Otherwise send
- * MAX_SEND_SIZE bytes, but round back to logfile or page boundary.
+ * max_wal_send bytes to send, send everything. Otherwise send
+ * max_wal_send bytes, but round back to logfile or page boundary.
*
* The rounding is not only for performance reasons. Walreceiver relies on
* the fact that we never split a WAL record across two messages. Since a
@@ -2357,7 +2358,7 @@ XLogSendPhysical(void)
*/
startptr = sentPtr;
endptr = startptr;
- endptr += MAX_SEND_SIZE;
+ endptr += max_wal_send;
/* if we went beyond SendRqstPtr, back off */
if (SendRqstPtr <= endptr)
@@ -2376,7 +2377,7 @@ XLogSendPhysical(void)
}
nbytes = endptr - startptr;
- Assert(nbytes <= MAX_SEND_SIZE);
+ Assert(nbytes <= max_wal_send);
/*
* OK to read and send the slice.
diff --git a/src/backend/utils/misc/guc.c b/src/backend/utils/misc/guc.c
index 5b23dbf..b9a0c47 100644
--- a/src/backend/utils/misc/guc.c
+++ b/src/backend/utils/misc/guc.c
@@ -112,6 +112,7 @@ extern char *default_tablespace;
extern char *temp_tablespaces;
extern bool ignore_checksum_failure;
extern bool synchronize_seqscans;
+extern int max_wal_send_guc;
#ifdef TRACE_SYNCSCAN
extern bool trace_syncscan;
@@ -2342,6 +2343,17 @@ static struct config_int ConfigureNamesInt[] =
},
{
+ {"max_wal_send", PGC_SIGHUP, REPLICATION_SENDING,
+ gettext_noop("Sets the maximum WAL payload size for WAL replication."),
+ NULL,
+ GUC_UNIT_KB
+ },
+ &max_wal_send_guc,
+ 128, 4, XLOG_SEG_SIZE / 1024,
+ NULL, NULL, NULL
+ },
+
+ {
{"commit_delay", PGC_SUSET, WAL_SETTINGS,
gettext_noop("Sets the delay in microseconds between transaction commit and "
"flushing WAL to disk."),
--
2.10.2
--
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