On Sun, Jun 9, 2013 at 1:22 AM, Nguyễn Thái Ngọc Duy <pclouds@xxxxxxxxx> 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@xxxxxxxxx>
> ---
> 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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