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[PATCH 06/15] run-job: auto-size or use custom pack-files batch

From
Derrick Stolee via GitGitGadget <gitgitgadget@gmail.com>
Date
Apr 3, 2020, 20:48 UTC
Message-ID
<c39a35a959e485623aacdbbecc1fce7d16a956c9.1585946894.git.gitgitgadget@gmail.com>
In-Reply-To
<pull.597.git.1585946894.gitgitgadget@gmail.com>
From: Derrick Stolee <dstolee@microsoft.com>

When repacking during the 'pack-files' job, we use the --batch-size option in 'git multi-pack-index repack'. The initial setting used --batch-size=0 to repack everything into a single pack-file. This is not sustaintable for a large repository. The amount of work required is also likely to use too many system resources for a background job.

Update the 'git run-job pack-files' command by allowing a direct --batch-size option that can change the value provided. Update the default of "0" to a computed size based on the existing pack-files. While computing that new size, count the existing pack-files and skip the repack step if there are at most two pack-files.

The dynamic default size is computed with this idea in mind for a client repository that was cloned from a very large remote: there is likely one "big" pack-file that was created at clone time. Thus, do not try repacking it as it is likely packed efficiently by the server. Instead, try packing the other pack-files into a single pack-file.

The size is then computed as follows:
	batch size = total size - max pack size

The batch size is then also limited to be at most two gigabytes. This serves two purposes. First, having a limit prevents doing too much work when the repository is extremely large. Pack-files larger than two gigabytes are likely to either contain large blobs or have been carefully repacked by a previous repack operation. Second, two gigabytes is the size limit for a signed 32-bit int. It's a good limit to consider, and to keep it far away from the unsigned 32-bit int limit. This limit comes to mind because on Windows an "unsigned long" is 32 bits and OPT_MAGNITUDE() uses unsigned longs for its parsing logic.

This calculation mimics a similar calculation in Scalar [1], except for a 3% drop in the calculated batch size due to the round-off error that can happen with the "expected size" calculation for a pack-file.

[1] https://github.com/microsoft/scalar/blob/616e9b16dd120b8fdb652d6d5a55618c731a8aea/Scalar.Common/Maintenance/PackfileMaintenanceStep.cs#L141-L143
Signed-off-by: Derrick Stolee <dstolee@microsoft.com>
---
 Documentation/git-run-job.txt | 13 +++--
 builtin/run-job.c             | 90 ++++++++++++++++++++++++++++++++---
 t/t7900-run-job.sh            |  6 ++-
 3 files changed, 96 insertions(+), 13 deletions(-)
diff --git a/Documentation/git-run-job.txt b/Documentation/git-run-job.txt
index 108ed25b8bd..cdd6417f7c9 100644
--- a/Documentation/git-run-job.txt
+++ b/Documentation/git-run-job.txt
@@ -9,7 +9,7 @@ git-run-job - Run a maintenance job. Intended for background operation.
 SYNOPSIS
 --------
 [verse]
-'git run-job (commit-graph|fetch|loose-objects|pack-files)'
+'git run-job (commit-graph|fetch|loose-objects|pack-files) [<options>]'
 
 
 DESCRIPTION
@@ -82,9 +82,14 @@ only happens if all objects in the pack-file are also stored in a newer
 pack-file. Second, it selects a group of pack-files whose "expected
 size" is below the batch size until the group has total expected size at
 least the batch size; see the `--batch-size` option for the `repack`
-subcommand in linkgit:git-multi-pack-index[1]. The default batch-size is
-zero, which is a special case that attempts to repack all pack-files
-into a single pack-file.
+subcommand in linkgit:git-multi-pack-index[1].
++
+The default batch size is computed to optimize for having a single large
+pack-file and many small pack-files. When there are two or fewer
+pack-files, the job does not attempt to repack. Otherwise, the batch
+size is the sum of all pack-file sizes minus the largest pack-file size.
+The batch size is capped at two gigabytes. This intends to pack all
+small pack-files into a single pack-file.
 
 
 GIT
diff --git a/builtin/run-job.c b/builtin/run-job.c
index d3543f7ccb9..2ccc3bbae2d 100644
--- a/builtin/run-job.c
+++ b/builtin/run-job.c
@@ -3,12 +3,18 @@
 #include "commit-graph.h"
 #include "midx.h"
 #include "object-store.h"
+#include "packfile.h"
 #include "parse-options.h"
 #include "repository.h"
 #include "run-command.h"
 
 static char const * const builtin_run_job_usage[] = {
-	N_("git run-job (commit-graph|fetch|loose-objects|pack-files)"),
+	N_("git run-job (commit-graph|fetch|loose-objects|pack-files) [<options>]"),
+	NULL
+};
+
+static char const * const builtin_run_job_pack_file_usage[] = {
+	N_("git run-job pack-files [--batch-size=<size>]"),
 	NULL
 };
 
@@ -278,15 +284,74 @@ static int multi_pack_index_expire(void)
 	return run_command_v_opt(cmd.argv, RUN_GIT_CMD);
 }
 
-static int multi_pack_index_repack(void)
+#define TWO_GIGABYTES (2147483647)
+
+static off_t get_auto_pack_size(int *count)
+{
+	/*
+	 * The "auto" value is special: we optimize for
+	 * one large pack-file (i.e. from a clone) and
+	 * expect the rest to be small and they can be
+	 * repacked quickly. Find the sum of the sizes
+	 * other than the largest pack-file, then use
+	 * that as the batch size.
+	 */
+	off_t total_size = 0;
+	off_t max_size = 0;
+	off_t result_size;
+	struct packed_git *p;
+
+	*count = 0;
+
+	reprepare_packed_git(the_repository);
+	for (p = get_all_packs(the_repository); p; p = p->next) {
+		(*count)++;
+		total_size += p->pack_size;
+
+		if (p->pack_size > max_size)
+			max_size = p->pack_size;
+	}
+
+	result_size = total_size - max_size;
+
+	/* But limit ourselves to a batch size of 2g */
+	if (result_size > TWO_GIGABYTES)
+		result_size = TWO_GIGABYTES;
+
+	return result_size;
+}
+
+#define UNSET_BATCH_SIZE ((unsigned long)-1)
+static int multi_pack_index_repack(unsigned long batch_size)
 {
 	int result;
 	struct argv_array cmd = ARGV_ARRAY_INIT;
+	struct strbuf batch_arg = STRBUF_INIT;
+	int count;
+	off_t default_size = get_auto_pack_size(&count);
+
+	if (count <= 2)
+		return 0;
+
+	strbuf_addstr(&batch_arg, "--batch-size=");
+
+	if (batch_size != UNSET_BATCH_SIZE)
+		strbuf_addf(&batch_arg, "\"%"PRIuMAX"\"", (uintmax_t)batch_size);
+	else
+		strbuf_addf(&batch_arg, "%"PRIuMAX,
+			    (uintmax_t)default_size);
+
 	argv_array_pushl(&cmd, "multi-pack-index", "repack",
-			 "--no-progress", "--batch-size=0", NULL);
+			 "--no-progress", batch_arg.buf, NULL);
 	result = run_command_v_opt(cmd.argv, RUN_GIT_CMD);
 
-	if (result && multi_pack_index_verify()) {
+	strbuf_release(&batch_arg);
+
+	/*
+	 * Verify here to avoid verifying again when there are two
+	 * or fewer pack-files.
+	 */
+	if (!result && multi_pack_index_verify()) {
 		warning(_("multi-pack-index verify failed after repack"));
 		result = rewrite_multi_pack_index();
 	}
@@ -294,8 +359,19 @@ static int multi_pack_index_repack(void)
 	return result;
 }
 
-static int run_pack_files_job(void)
+static int run_pack_files_job(int argc, const char **argv)
 {
+	static unsigned long batch_size = UNSET_BATCH_SIZE;
+	static struct option builtin_run_job_pack_file_options[] = {
+		OPT_MAGNITUDE(0, "batch-size", &batch_size,
+			      N_("specify a batch-size for the incremental repack")),
+		OPT_END(),
+	};
+
+	argc = parse_options(argc, argv, NULL,
+			     builtin_run_job_pack_file_options,
+			     builtin_run_job_pack_file_usage, 0);
+
 	if (multi_pack_index_write()) {
 		error(_("failed to write multi-pack-index"));
 		return 1;
@@ -316,7 +392,7 @@ static int run_pack_files_job(void)
 		return rewrite_multi_pack_index();
 	}
 
-	if (multi_pack_index_repack()) {
+	if (multi_pack_index_repack(batch_size)) {
 		error(_("multi-pack-index repack failed"));
 		return 1;
 	}
@@ -348,7 +424,7 @@ int cmd_run_job(int argc, const char **argv, const char *prefix)
 		if (!strcmp(argv[0], "loose-objects"))
 			return run_loose_objects_job();
 		if (!strcmp(argv[0], "pack-files"))
-			return run_pack_files_job();
+			return run_pack_files_job(argc, argv);
 	}
 
 	usage_with_options(builtin_run_job_usage,
diff --git a/t/t7900-run-job.sh b/t/t7900-run-job.sh
index 416ba04989d..2d9f6cdf328 100755
--- a/t/t7900-run-job.sh
+++ b/t/t7900-run-job.sh
@@ -128,8 +128,10 @@ test_expect_success 'pack-files job' '
 	# the job deletes the two old packs, and does not write
 	# a new one because only one pack remains.
 	git -C client run-job pack-files &&
-	ls client/.git/objects/pack/*.pack >packs-after &&
-	test_line_count = 1 packs-after
+	ls client/$packDir/*.pack >packs-after &&
+	test_line_count = 2 packs-after &&
+	cat packs-after | grep "pack/test-1-" &&
+	cat packs-after | grep "pack/pack-"
 '
 
 test_done

-- 
gitgitgadget
Previous: Josh SteadmonNext: Derrick Stolee via GitGitGadget
Message 20 of 55 in “[RFC] Maintenance jobs and job runner”
  1. 00/15 [RFC] Maintenance jobs and job runnerDerrick Stolee via GitGitGadget, Apr 3, 2020
  2. 01/15 run-job: create barebones builtinDerrick Stolee via GitGitGadget, Apr 3, 2020
  3. Phillip WoodApr 5, 2020
  4. Junio C HamanoApr 5, 2020
  5. Derrick StoleeApr 6, 2020
  6. Danh DoanApr 7, 2020
  7. Derrick StoleeApr 7, 2020
  8. Danh DoanApr 7, 2020
  9. Johannes SchindelinApr 7, 2020
  10. 02/15 run-job: implement commit-graph jobDerrick Stolee via GitGitGadget, Apr 3, 2020
  11. Josh SteadmonMay 20, 2020
  12. 05/15 run-job: implement pack-files jobDerrick Stolee via GitGitGadget, Apr 3, 2020
  13. Josh SteadmonMay 27, 2020
  14. 03/15 run-job: implement fetch jobDerrick Stolee via GitGitGadget, Apr 3, 2020
  15. Phillip WoodApr 5, 2020
  16. Derrick StoleeApr 6, 2020
  17. Junio C HamanoApr 5, 2020
  18. Derrick StoleeApr 6, 2020
  19. Josh SteadmonMay 20, 2020
  20. 06/15 run-job: auto-size or use custom pack-files batchDerrick Stolee via GitGitGadget, Apr 3, 2020
  21. 04/15 run-job: implement loose-objects jobDerrick Stolee via GitGitGadget, Apr 3, 2020
  22. Junio C HamanoApr 5, 2020
  23. 09/15 job-runner: load repos from config by defaultDerrick Stolee via GitGitGadget, Apr 3, 2020
  24. Phillip WoodApr 5, 2020
  25. Derrick StoleeApr 6, 2020
  26. Phillip WoodApr 5, 2020
  27. Derrick StoleeApr 6, 2020
  28. 08/15 job-runner: create builtin for job loopDerrick Stolee via GitGitGadget, Apr 3, 2020
  29. 11/15 job-runner: use config for loop intervalDerrick Stolee via GitGitGadget, Apr 3, 2020
  30. 10/15 job-runner: use config to limit job frequencyDerrick Stolee via GitGitGadget, Apr 3, 2020
  31. Phillip WoodApr 5, 2020
  32. 13/15 job-runner: skip a job if job.<job-name>.enabled is falseDerrick Stolee via GitGitGadget, Apr 3, 2020
  33. 14/15 job-runner: add --daemonize optionDerrick Stolee via GitGitGadget, Apr 3, 2020
  34. 12/15 job-runner: add --interval=<span> optionDerrick Stolee via GitGitGadget, Apr 3, 2020
  35. 07/15 config: add job.pack-files.batchSize optionDerrick Stolee via GitGitGadget, Apr 3, 2020
  36. 15/15 runjob: customize the loose-objects batch sizeDerrick Stolee via GitGitGadget, Apr 3, 2020
  37. Junio C HamanoApr 3, 2020
  38. Derrick StoleeApr 4, 2020
  39. Danh DoanApr 7, 2020
  40. Derrick StoleeApr 7, 2020
  41. Danh DoanApr 7, 2020
  42. Johannes SchindelinApr 7, 2020
  43. brian m. carlsonApr 7, 2020
  44. Junio C HamanoApr 7, 2020
  45. Johannes SchindelinApr 7, 2020
  46. brian m. carlsonApr 8, 2020
  47. Josh SteadmonMay 27, 2020
  48. Junio C HamanoMay 28, 2020
  49. Johannes SchindelinMay 27, 2020
  50. Junio C HamanoMay 28, 2020
  51. Jonathan NiederMay 28, 2020
  52. Junio C HamanoMay 28, 2020
  53. Jonathan NiederMay 28, 2020
  54. Derrick StoleeMay 28, 2020
  55. Johannes SchindelinMay 28, 2020

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