core: use env variable instead of config var to turn on logging pack access

5f44324 (core: log offset pack data accesses happened - 2011-07-06)
provides a way to observe pack access patterns via a config
switch. Setting an environment variable looks more obvious than a
config var, especially when you just need to _observe_, and more
inline with other tracing knobs we have.

Document it as it may be useful for remote troubleshooting.

Signed-off-by: Nguyễn Thái Ngọc Duy <pclouds@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

diff --git a/Documentation/git.txt b/Documentation/git.txt
index 9e302b0..3e74440 100644 (file)
--- a/Documentation/git.txt
+++ b/Documentation/git.txt
@@ -832,6 +832,13 @@ for further details.
        as a file path and will try to write the trace messages
        into it.
 
+'GIT_TRACE_PACK_ACCESS'::
+       If this variable is set to a path, a file will be created at
+       the given path logging all accesses to any packs. For each
+       access, the pack file name and an offset in the pack is
+       recorded. This may be helpful for troubleshooting some
+       pack-related performance problems.
+
 GIT_LITERAL_PATHSPECS::
        Setting this variable to `1` will cause Git to treat all
        pathspecs literally, rather than as glob patterns. For example,

diff --git a/cache.h b/cache.h
index 94ca1ac..9bfd76b 100644 (file)
--- a/cache.h
+++ b/cache.h
@@ -772,9 +772,6 @@ extern int parse_sha1_header(const char *hdr, unsigned long *sizep);
 /* global flag to enable extra checks when accessing packed objects */
 extern int do_check_packed_object_crc;
 
-/* for development: log offset of pack access */
-extern const char *log_pack_access;
-
 extern int check_sha1_signature(const unsigned char *sha1, void *buf, unsigned long size, const char *type);
 
 extern int move_temp_to_file(const char *tmpfile, const char *filename);

diff --git a/config.c b/config.c
index aefd80b..ce074d7 100644 (file)
--- a/config.c
+++ b/config.c
@@ -675,9 +675,6 @@ static int git_default_core_config(const char *var, const char *value)
                return 0;
        }
 
-       if (!strcmp(var, "core.logpackaccess"))
-               return git_config_string(&log_pack_access, var, value);
-
        if (!strcmp(var, "core.autocrlf")) {
                if (value && !strcasecmp(value, "input")) {
                        if (core_eol == EOL_CRLF)

diff --git a/environment.c b/environment.c
index e2e75c1..0cb67b2 100644 (file)
--- a/environment.c
+++ b/environment.c
@@ -37,7 +37,6 @@ size_t packed_git_window_size = DEFAULT_PACKED_GIT_WINDOW_SIZE;
 size_t packed_git_limit = DEFAULT_PACKED_GIT_LIMIT;
 size_t delta_base_cache_limit = 16 * 1024 * 1024;
 unsigned long big_file_threshold = 512 * 1024 * 1024;
-const char *log_pack_access;
 const char *pager_program;
 int pager_use_color = 1;
 const char *editor_program;

diff --git a/sha1_file.c b/sha1_file.c
index 67e815b..7fa62c2 100644 (file)
--- a/sha1_file.c
+++ b/sha1_file.c
@@ -36,6 +36,9 @@ static inline uintmax_t sz_fmt(size_t s) { return s; }
 
 const unsigned char null_sha1[20];
 
+static const char *no_log_pack_access = "no_log_pack_access";
+static const char *log_pack_access;
+
 /*
  * This is meant to hold a *small* number of objects that you would
  * want read_sha1_file() to be able to return, but yet you do not want
@@ -1956,12 +1959,19 @@ static void write_pack_access_log(struct packed_git *p, off_t obj_offset)
 {
        static FILE *log_file;
 
+       if (!log_pack_access)
+               log_pack_access = getenv("GIT_TRACE_PACK_ACCESS");
+       if (!log_pack_access)
+               log_pack_access = no_log_pack_access;
+       if (log_pack_access == no_log_pack_access)
+               return;
+
        if (!log_file) {
                log_file = fopen(log_pack_access, "w");
                if (!log_file) {
                        error("cannot open pack access log '%s' for writing: %s",
                              log_pack_access, strerror(errno));
-                       log_pack_access = NULL;
+                       log_pack_access = no_log_pack_access;
                        return;
                }
        }
@@ -1992,7 +2002,7 @@ void *unpack_entry(struct packed_git *p, off_t obj_offset,
        int delta_stack_nr = 0, delta_stack_alloc = UNPACK_ENTRY_STACK_PREALLOC;
        int base_from_cache = 0;
 
-       if (log_pack_access)
+       if (log_pack_access != no_log_pack_access)
                write_pack_access_log(p, obj_offset);
 
        /* PHASE 1: drill down to the innermost base object */