Speed up index file writing by chunking it nicely.

No point in making 17,000 small writes when you can make just
a couple of hundred nice 8kB writes instead and save a lot
of time.

diff --git a/read-cache.c b/read-cache.c
index bfa2de7..c3beb67 100644 (file)
--- a/read-cache.c
+++ b/read-cache.c
@@ -227,6 +227,42 @@ unmap:
        return error("verify header failed");
 }
 
+#define WRITE_BUFFER_SIZE 8192
+static char write_buffer[WRITE_BUFFER_SIZE];
+static unsigned long write_buffer_len;
+
+static int ce_write(int fd, void *data, unsigned int len)
+{
+       while (len) {
+               unsigned int buffered = write_buffer_len;
+               unsigned int partial = WRITE_BUFFER_SIZE - buffered;
+               if (partial > len)
+                       partial = len;
+               memcpy(write_buffer + buffered, data, partial);
+               buffered += partial;
+               if (buffered == WRITE_BUFFER_SIZE) {
+                       if (write(fd, write_buffer, WRITE_BUFFER_SIZE) != WRITE_BUFFER_SIZE)
+                               return -1;
+                       buffered = 0;
+               }
+               write_buffer_len = buffered;
+               len -= partial;
+               data += partial;
+       }
+       return 0;
+}
+
+static int ce_flush(int fd)
+{
+       unsigned int left = write_buffer_len;
+       if (left) {
+               write_buffer_len = 0;
+               if (write(fd, write_buffer, left) != left)
+                       return -1;
+       }
+       return 0;
+}
+
 int write_cache(int newfd, struct cache_entry **cache, int entries)
 {
        SHA_CTX c;
@@ -246,14 +282,13 @@ int write_cache(int newfd, struct cache_entry **cache, int entries)
        }
        SHA1_Final(hdr.sha1, &c);
 
-       if (write(newfd, &hdr, sizeof(hdr)) != sizeof(hdr))
+       if (ce_write(newfd, &hdr, sizeof(hdr)) < 0)
                return -1;
 
        for (i = 0; i < entries; i++) {
                struct cache_entry *ce = cache[i];
-               int size = ce_size(ce);
-               if (write(newfd, ce, size) != size)
+               if (ce_write(newfd, ce, ce_size(ce)) < 0)
                        return -1;
        }
-       return 0;
+       return ce_flush(newfd);
 }