Re: [PATCH 1/2] core: use env variable instead of config var to turn on logging pack access

[Eric Sunshine <sunshine@sunshineco.com>]

On Sun, Jun 9, 2013 at 1:22 AM, Nguyễn Thái Ngọc Duy <pclouds@gmail.com> wrote:
> 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>
> ---
>  Documentation/git.txt |  7 +++++++
>  cache.h               |  3 ---
>  config.c              |  3 ---
>  environment.c         |  1 -
>  sha1_file.c           | 14 ++++++++++++--
>  5 files changed, 19 insertions(+), 9 deletions(-)
>
> diff --git a/Documentation/git.txt b/Documentation/git.txt
> index 68f1ee6..c760918 100644
> --- a/Documentation/git.txt
> +++ b/Documentation/git.txt
> @@ -838,6 +838,13 @@ 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 df532f8..4f41606 100644
> --- 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 7a85ebd..d04e815 100644
> --- a/config.c
> +++ b/config.c
> @@ -688,9 +688,6 @@ 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
> --- 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 b114cc9..4b23bb8 100644
> --- 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 */
> --
> 1.8.2.83.gc99314b
>
> --
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