Hold compressed filenames more efficiently in memory.

std::string::resize() will rarely give memory back, so allocate
the string with the right size to begin with. This means we don't
carry around a lot of slop, saving ~15% RAM during build.

diff --git a/plocate-build.cpp b/plocate-build.cpp
index 42ff96d20563758b4c2d9951118cf6e55c703d71..0580e4b455ee67f3698e78c976895c898252b8a9 100644 (file)
--- a/plocate-build.cpp
+++ b/plocate-build.cpp
@@ -123,14 +123,14 @@ void read_mlocate(const char *filename, vector<string> *files)
        close(fd);
 }
 
-string zstd_compress(const string &src)
+string zstd_compress(const string &src, string *tempbuf)
 {
        size_t max_size = ZSTD_compressBound(src.size());
-       string dst;
-       dst.resize(max_size);
-       size_t size = ZSTD_compress(&dst[0], max_size, src.data(), src.size(), /*level=*/6);
-       dst.resize(size);
-       return dst;
+       if (tempbuf->size() < max_size) {
+               tempbuf->resize(max_size);
+       }
+       size_t size = ZSTD_compress(&(*tempbuf)[0], max_size, src.data(), src.size(), /*level=*/6);
+       return string(tempbuf->data(), size);
 }
 
 void do_build(const char *infile, const char *outfile, int block_size)
@@ -233,13 +233,12 @@ void do_build(const char *infile, const char *outfile, int block_size)
        string uncompressed_filenames;
        int num_files_this_block = 0;
 
-       string dst;
-
+       string dst, tempbuf;
        for (string &filename : files) {
                uncompressed_filenames += filename;
                filename.clear();
                if (++num_files_this_block == block_size) {
-                       filename_blocks.push_back(zstd_compress(uncompressed_filenames));
+                       filename_blocks.push_back(zstd_compress(uncompressed_filenames, &tempbuf));
                        uncompressed_filenames.clear();
                        num_files_this_block = 0;
                } else {
@@ -247,7 +246,7 @@ void do_build(const char *infile, const char *outfile, int block_size)
                }
        }
        if (num_files_this_block > 0) {
-               filename_blocks.push_back(zstd_compress(uncompressed_filenames));
+               filename_blocks.push_back(zstd_compress(uncompressed_filenames, &tempbuf));
        }
        files.clear();