[PATCH v4 0/2] reftable/stack: use geometric table compaction
- From
Justin Tobler via GitGitGadget <gitgitgadget@gmail.com>
- Date
- Apr 3, 2024, 00:20 UTC
- Message-ID
- <pull.1683.v4.git.1712103636.gitgitgadget@gmail.com>
- In-Reply-To
- <pull.1683.v3.git.1711685809.gitgitgadget@gmail.com>
Hello again,
This is the fourth version my patch series that refactors the reftable compaction strategy to instead follow a geometric sequence. Changes compared to v3:
* Changed env name from GIT_TEST_REFTABLE_NO_AUTOCOMPACTION to GIT_TEST_REFTABLE_AUTOCOMPACTION and set the default to false. This should hopefully be a bit more intuitive since it avoids the double negative. * Updated the corresponding env var test in t0610-reftable-basics.sh to assert on the number of tables added and be overall less fragile. * Folded lines that were too long. * Updated some comments in stack.c to more accurately explain that table segment end is exclusive. * Dropped reftable/stack: make segment end inclusive commit to keep segment end exclusive and better follow expectations.
Thanks for taking a look!
-Justin
Justin Tobler (2): reftable/stack: add env to disable autocompaction reftable/stack: use geometric table compaction
reftable/stack.c | 126 +++++++++++++++++++------------------ reftable/stack.h | 3 - reftable/stack_test.c | 66 ++++--------------- reftable/system.h | 1 + t/t0610-reftable-basics.sh | 65 +++++++++++++++---- 5 files changed, 132 insertions(+), 129 deletions(-)
base-commit: c75fd8d8150afdf836b63a8e0534d9b9e3e111ba Published-As: https://github.com/gitgitgadget/git/releases/tag/pr-1683%2Fjltobler%2Fjt%2Freftable-geometric-compaction-v4 Fetch-It-Via: git fetch https://github.com/gitgitgadget/git pr-1683/jltobler/jt/reftable-geometric-compaction-v4 Pull-Request: https://github.com/gitgitgadget/git/pull/1683
Range-diff vs v3:
1: 2fdd8ea1133 ! 1: 2a0421e5f20 reftable/stack: add env to disable autocompaction
@@ Commit message
In future tests it will be neccesary to create repositories with a set
number of tables. To make this easier, introduce the
- `GIT_TEST_REFTABLE_NO_AUTOCOMPACTION` environment variable that, when
- set, disables autocompaction of reftables.
+ `GIT_TEST_REFTABLE_AUTOCOMPACTION` environment variable that, when set
+ to false, disables autocompaction of reftables.
Signed-off-by: Justin Tobler <jltobler@gmail.com>
@@ reftable/stack.c: int reftable_addition_commit(struct reftable_addition *add)
goto done;
- if (!add->stack->disable_auto_compact)
-+ if (!add->stack->disable_auto_compact && !git_env_bool("GIT_TEST_REFTABLE_NO_AUTOCOMPACTION", 0))
++ if (!add->stack->disable_auto_compact &&
++ git_env_bool("GIT_TEST_REFTABLE_AUTOCOMPACTION", 1))
err = reftable_stack_auto_compact(add->stack);
done:
@@ t/t0610-reftable-basics.sh: test_expect_success 'ref transaction: writes cause a
test_line_count = 1 repo/.git/reftable/tables.list
'
-+test_expect_success 'ref transaction: environment variable disables auto-compaction' '
++test_expect_success 'ref transaction: env var disables compaction' '
+ test_when_finished "rm -rf repo" &&
+
+ git init repo &&
+ test_commit -C repo A &&
-+ for i in $(test_seq 20)
++
++ start=$(wc -l <repo/.git/reftable/tables.list) &&
++ iterations=5 &&
++ expected=$((start + iterations)) &&
++
++ for i in $(test_seq $iterations)
+ do
-+ GIT_TEST_REFTABLE_NO_AUTOCOMPACTION=true git -C repo update-ref branch-$i HEAD || return 1
++ GIT_TEST_REFTABLE_AUTOCOMPACTION=false \
++ git -C repo update-ref branch-$i HEAD || return 1
+ done &&
-+ test_line_count = 23 repo/.git/reftable/tables.list &&
++ test_line_count = $expected repo/.git/reftable/tables.list &&
+
+ git -C repo update-ref foo HEAD &&
-+ test_line_count = 1 repo/.git/reftable/tables.list
++ test_line_count -lt $expected repo/.git/reftable/tables.list
+'
+
check_fsync_events () {
2: 7e62c2286ae ! 2: e0f4d0dbcc1 reftable/stack: use geometric table compaction
@@ reftable/stack.c: static int segment_size(struct segment *s)
- if (fastlog2(min_seg.bytes) < fastlog2(sizes[prev]))
+ /*
+ * Find the ending table of the compaction segment needed to restore the
-+ * geometric sequence.
++ * geometric sequence. Note that the segment end is exclusive.
+ *
+ * To do so, we iterate backwards starting from the most recent table
+ * until a valid segment end is found. If the preceding table is smaller
+ * than the current table multiplied by the geometric factor (2), the
-+ * current table is set as the compaction segment end.
++ * compaction segment end has been identified.
+ *
+ * Tables after the ending point are not added to the byte count because
+ * they are already valid members of the geometric sequence. Due to the
@@ reftable/stack.c: static int segment_size(struct segment *s)
+ * Example table size sequence requiring no compaction:
+ * 64, 32, 16, 8, 4, 2, 1
+ *
-+ * Example compaction segment end set to table with size 3:
++ * Example table size sequence where compaction segment end is set to
++ * the last table. Since the segment end is exclusive, the last table is
++ * excluded during subsequent compaction and the table with size 3 is
++ * the final table included:
+ * 64, 32, 16, 8, 4, 3, 1
+ */
+ for (i = n - 1; i > 0; i--) {
@@ reftable/stack_test.c: static void test_empty_add(void)
+ int l = 0;
+ if (sz == 0)
+ return 0;
-+ for (; sz; sz /= 2) {
++ for (; sz; sz /= 2)
+ l++;
-+ }
+ return l - 1;
+}
+
@@ t/t0610-reftable-basics.sh: test_expect_success 'ref transaction: writes cause a
test_commit -C repo --no-tag B &&
test_line_count = 1 repo/.git/reftable/tables.list
-@@ t/t0610-reftable-basics.sh: test_expect_success 'ref transaction: environment variable disables auto-compact
- do
- GIT_TEST_REFTABLE_NO_AUTOCOMPACTION=true git -C repo update-ref branch-$i HEAD || return 1
- done &&
-- test_line_count = 23 repo/.git/reftable/tables.list &&
-+ test_line_count = 22 repo/.git/reftable/tables.list &&
-
- git -C repo update-ref foo HEAD &&
- test_line_count = 1 repo/.git/reftable/tables.list
+@@ t/t0610-reftable-basics.sh: test_expect_success 'ref transaction: env var disables compaction' '
+ test_line_count -lt $expected repo/.git/reftable/tables.list
'
+test_expect_success 'ref transaction: alternating table sizes are compacted' '
+ test_when_finished "rm -rf repo" &&
++
+ git init repo &&
+ test_commit -C repo A &&
-+ for i in $(test_seq 20)
++ for i in $(test_seq 5)
+ do
+ git -C repo branch -f foo &&
+ git -C repo branch -d foo || return 1
@@ t/t0610-reftable-basics.sh: test_expect_success 'worktree: pack-refs in main rep
test_when_finished "rm -rf repo worktree" &&
git init repo &&
test_commit -C repo A &&
-- git -C repo worktree add ../worktree &&
-+ GIT_TEST_REFTABLE_NO_AUTOCOMPACTION=true git -C repo worktree add ../worktree &&
-+ GIT_TEST_REFTABLE_NO_AUTOCOMPACTION=true git -C worktree update-ref refs/worktree/per-worktree HEAD &&
++
++ GIT_TEST_REFTABLE_AUTOCOMPACTION=false \
+ git -C repo worktree add ../worktree &&
++ GIT_TEST_REFTABLE_AUTOCOMPACTION=false \
++ git -C worktree update-ref refs/worktree/per-worktree HEAD &&
- test_line_count = 3 repo/.git/worktrees/worktree/reftable/tables.list &&
- test_line_count = 4 repo/.git/reftable/tables.list &&
@@ t/t0610-reftable-basics.sh: test_expect_success 'worktree: pack-refs in worktree
test_when_finished "rm -rf repo worktree" &&
git init repo &&
test_commit -C repo A &&
-- git -C repo worktree add ../worktree &&
-+ GIT_TEST_REFTABLE_NO_AUTOCOMPACTION=true git -C repo worktree add ../worktree &&
-+ GIT_TEST_REFTABLE_NO_AUTOCOMPACTION=true git -C worktree update-ref refs/worktree/per-worktree HEAD &&
++
++ GIT_TEST_REFTABLE_AUTOCOMPACTION=false \
+ git -C repo worktree add ../worktree &&
++ GIT_TEST_REFTABLE_AUTOCOMPACTION=false \
++ git -C worktree update-ref refs/worktree/per-worktree HEAD &&
- test_line_count = 3 repo/.git/worktrees/worktree/reftable/tables.list &&
- test_line_count = 4 repo/.git/reftable/tables.list &&
@@ t/t0610-reftable-basics.sh: test_expect_success 'worktree: pack-refs in worktree
'
test_expect_success 'worktree: creating shared ref updates main stack' '
- test_when_finished "rm -rf repo worktree" &&
- git init repo &&
- test_commit -C repo A &&
-+ test_commit -C repo B &&
-
- git -C repo worktree add ../worktree &&
- git -C repo pack-refs &&
@@ t/t0610-reftable-basics.sh: test_expect_success 'worktree: creating shared ref updates main stack' '
test_line_count = 1 repo/.git/worktrees/worktree/reftable/tables.list &&
test_line_count = 1 repo/.git/reftable/tables.list &&
-- git -C worktree update-ref refs/heads/shared HEAD &&
-+ GIT_TEST_REFTABLE_NO_AUTOCOMPACTION=true git -C worktree update-ref refs/heads/shared HEAD &&
++ GIT_TEST_REFTABLE_AUTOCOMPACTION=false \
+ git -C worktree update-ref refs/heads/shared HEAD &&
test_line_count = 1 repo/.git/worktrees/worktree/reftable/tables.list &&
test_line_count = 2 repo/.git/reftable/tables.list
- '
3: 9a33914c852 < -: ----------- reftable/stack: make segment end inclusive-- gitgitgadget