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authorLibravatar John Cai <johncai86@gmail.com>2022-02-18 18:23:14 +0000
committerLibravatar Junio C Hamano <gitster@pobox.com>2022-02-18 11:21:46 -0800
commit440c705ea63253642c8f4761f80eb7a97a62b614 (patch)
tree105a53ee847d3c47d9d92aaac93f6badeb49f2ad /t/t5100/info0003
parentcat-file: add remove_timestamp helper (diff)
downloadtgif-440c705ea63253642c8f4761f80eb7a97a62b614.tar.xz
cat-file: add --batch-command mode
Add a new flag --batch-command that accepts commands and arguments from stdin, similar to git-update-ref --stdin. At GitLab, we use a pair of long running cat-file processes when accessing object content. One for iterating over object metadata with --batch-check, and the other to grab object contents with --batch. However, if we had --batch-command, we wouldn't need to keep both processes around, and instead just have one --batch-command process where we can flip between getting object info, and getting object contents. Since we have a pair of cat-file processes per repository, this means we can get rid of roughly half of long lived git cat-file processes. Given there are many repositories being accessed at any given time, this can lead to huge savings. git cat-file --batch-command will enter an interactive command mode whereby the user can enter in commands and their arguments that get queued in memory: <command1> [arg1] [arg2] LF <command2> [arg1] [arg2] LF When --buffer mode is used, commands will be queued in memory until a flush command is issued that execute them: flush LF The reason for a flush command is that when a consumer process (A) talks to a git cat-file process (B) and interactively writes to and reads from it in --buffer mode, (A) needs to be able to control when the buffer is flushed to stdout. Currently, from (A)'s perspective, the only way is to either 1. kill (B)'s process 2. send an invalid object to stdin. 1. is not ideal from a performance perspective as it will require spawning a new cat-file process each time, and 2. is hacky and not a good long term solution. With this mechanism of queueing up commands and letting (A) issue a flush command, process (A) can control when the buffer is flushed and can guarantee it will receive all of the output when in --buffer mode. --batch-command also will not allow (B) to flush to stdout until a flush is received. This patch adds the basic structure for adding command which can be extended in the future to add more commands. It also adds the following two commands (on top of the flush command): contents <object> LF info <object> LF The contents command takes an <object> argument and prints out the object contents. The info command takes an <object> argument and prints out the object metadata. These can be used in the following way with --buffer: info <object> LF contents <object> LF contents <object> LF info <object> LF flush LF info <object> LF flush LF When used without --buffer: info <object> LF contents <object> LF contents <object> LF info <object> LF info <object> LF Helped-by: Ævar Arnfjörð Bjarmason <avarab@gmail.com> Signed-off-by: John Cai <johncai86@gmail.com> Signed-off-by: Junio C Hamano <gitster@pobox.com>
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