From 0ecc814c8130a2258cdd108e1fc22edb399e8246 Mon Sep 17 00:00:00 2001
From: "zhaozhao.zz" <276441700@qq.com>
Date: Mon, 17 May 2021 21:57:17 +0800
Subject: [PATCH] AOF: remove memmove in aofChildWriteDiffData and record the
 latency (#5362)

Improve performance by avoiding inefficiencies in the parent process during AOFRW.
* AOF: record the latency of aofChildWriteDiffData
* AOF: avoid memmove in aofChildWriteDiffData
---
 src/aof.c | 27 +++++++++++++++------------
 1 file changed, 15 insertions(+), 12 deletions(-)

diff --git a/src/aof.c b/src/aof.c
index 0d2971eac..35856f49b 100644
--- a/src/aof.c
+++ b/src/aof.c
@@ -60,7 +60,7 @@ void aofClosePipes(void);
 #define AOF_RW_BUF_BLOCK_SIZE (1024*1024*10)    /* 10 MB per block */
 
 typedef struct aofrwblock {
-    unsigned long used, free;
+    unsigned long used, free, pos;
     char buf[AOF_RW_BUF_BLOCK_SIZE];
 } aofrwblock;
 
@@ -96,29 +96,31 @@ void aofChildWriteDiffData(aeEventLoop *el, int fd, void *privdata, int mask) {
     listNode *ln;
     aofrwblock *block;
     ssize_t nwritten;
+    mstime_t latency;
     UNUSED(el);
     UNUSED(fd);
     UNUSED(privdata);
     UNUSED(mask);
 
+    latencyStartMonitor(latency);
     while(1) {
         ln = listFirst(server.aof_rewrite_buf_blocks);
         block = ln ? ln->value : NULL;
         if (server.aof_stop_sending_diff || !block) {
             aeDeleteFileEvent(server.el,server.aof_pipe_write_data_to_child,
                               AE_WRITABLE);
-            return;
+            break;
         }
-        if (block->used > 0) {
+        if (block->used != block->pos) {
             nwritten = write(server.aof_pipe_write_data_to_child,
-                             block->buf,block->used);
-            if (nwritten <= 0) return;
-            memmove(block->buf,block->buf+nwritten,block->used-nwritten);
-            block->used -= nwritten;
-            block->free += nwritten;
+                             block->buf+block->pos,block->used-block->pos);
+            if (nwritten <= 0) break;
+            block->pos += nwritten;
         }
-        if (block->used == 0) listDelNode(server.aof_rewrite_buf_blocks,ln);
+        if (block->used == block->pos) listDelNode(server.aof_rewrite_buf_blocks,ln);
     }
+    latencyEndMonitor(latency);
+    latencyAddSampleIfNeeded("aof-rewrite-write-data-to-child",latency);
 }
 
 /* Append data to the AOF rewrite buffer, allocating new blocks if needed. */
@@ -146,6 +148,7 @@ void aofRewriteBufferAppend(unsigned char *s, unsigned long len) {
             block = zmalloc(sizeof(*block));
             block->free = AOF_RW_BUF_BLOCK_SIZE;
             block->used = 0;
+            block->pos = 0;
             listAddNodeTail(server.aof_rewrite_buf_blocks,block);
 
             /* Log every time we cross more 10 or 100 blocks, respectively
@@ -181,9 +184,9 @@ ssize_t aofRewriteBufferWrite(int fd) {
         aofrwblock *block = listNodeValue(ln);
         ssize_t nwritten;
 
-        if (block->used) {
-            nwritten = write(fd,block->buf,block->used);
-            if (nwritten != (ssize_t)block->used) {
+        if (block->used != block->pos) {
+            nwritten = write(fd,block->buf+block->pos,block->used-block->pos);
+            if (nwritten != (ssize_t)(block->used-block->pos)) {
                 if (nwritten == 0) errno = EIO;
                 return -1;
             }