From e1c52539510131b498087e177fe93d0bac744a5b Mon Sep 17 00:00:00 2001 From: Johan Herland Date: Mon, 3 Feb 2020 22:04:44 +0100 Subject: t3305: check notes fanout more carefully and robustly In short, before this patch, this test script: - creates many notes - verifies that all notes in the notes tree has a fanout of 1 - removes most notes - verifies that the notes in the notes tree now has a fanout of 0 The fanout verification only happened twice: after creating all the notes, and after removing most of them. This patch strengthens the test by checking the fanout after _each_ added/removed note: We assert that the switch from fanout 0 -> 1 happens exactly once while adding notes (and that the switch pervades the entire notes tree). Likewise, we assert that the switch from fanout 1 -> 0 happens exactly once while removing notes. Additionally, we decrease the number of notes left after removal, from 50 to 15 notes, in order to ensure that fanout 1 -> 0 transition keeps happening regardless of external factors[1]. [1]: Currently (with the SHA1 hash function and the deterministic object ids of the test environment) the fanout heuristic in the notes code happens to switch from 0 -> 1 at 109 notes, and from 1 -> 0 at 59 notes. However, changing the hash function or other external factors will vary these numbers, and the latter may - in theory - go as low as 15. For more details, please see the discussion at https://public-inbox.org/git/20200125230035.136348-4-sandals@crustytoothpaste.net/ Cc: Johannes Schindelin Cc: Brian M. Carlson Signed-off-by: Johan Herland Signed-off-by: Junio C Hamano diff --git a/t/t3305-notes-fanout.sh b/t/t3305-notes-fanout.sh index 831f83d..402057c 100755 --- a/t/t3305-notes-fanout.sh +++ b/t/t3305-notes-fanout.sh @@ -4,6 +4,32 @@ test_description='Test that adding/removing many notes triggers automatic fanout . ./test-lib.sh +path_has_fanout() { + path=$1 && + fanout=$2 && + after_last_slash=$((40 - $fanout * 2)) && + echo $path | grep -q "^\([0-9a-f]\{2\}/\)\{$fanout\}[0-9a-f]\{$after_last_slash\}$" +} + +touched_one_note_with_fanout() { + notes_commit=$1 && + modification=$2 && # 'A' for addition, 'D' for deletion + fanout=$3 && + diff=$(git diff-tree --no-commit-id --name-status --root -r $notes_commit) && + path=$(echo $diff | sed -e "s/^$modification[\t ]//") && + path_has_fanout "$path" $fanout; +} + +all_notes_have_fanout() { + notes_commit=$1 && + fanout=$2 && + git ls-tree -r --name-only $notes_commit 2>/dev/null | + while read path + do + path_has_fanout $path $fanout || return 1 + done +} + test_expect_success 'creating many notes with git-notes' ' num_notes=300 && i=0 && @@ -20,7 +46,7 @@ test_expect_success 'creating many notes with git-notes' ' test_expect_success 'many notes created correctly with git-notes' ' git log | grep "^ " > output && - i=300 && + i=$num_notes && while test $i -gt 0 do echo " commit #$i" && @@ -30,34 +56,46 @@ test_expect_success 'many notes created correctly with git-notes' ' test_cmp expect output ' -test_expect_success 'many notes created with git-notes triggers fanout' ' - # Expect entire notes tree to have a fanout == 1 - git ls-tree -r --name-only refs/notes/commits | - while read path +test_expect_success 'stable fanout 0 is followed by stable fanout 1' ' + i=$num_notes && + fanout=0 && + while test $i -gt 0 do - echo $path | grep "^../[0-9a-f]*$" || { - echo "Invalid path \"$path\"" && - return 1; - } - done + i=$(($i - 1)) && + if touched_one_note_with_fanout refs/notes/commits~$i A $fanout + then + continue + elif test $fanout -eq 0 + then + fanout=1 && + if all_notes_have_fanout refs/notes/commits~$i $fanout + then + echo "Fanout 0 -> 1 at refs/notes/commits~$i" && + continue + fi + fi && + echo "Failed fanout=$fanout check at refs/notes/commits~$i" && + git ls-tree -r --name-only refs/notes/commits~$i && + return 1 + done && + all_notes_have_fanout refs/notes/commits 1 ' test_expect_success 'deleting most notes with git-notes' ' - num_notes=250 && + remove_notes=285 && i=0 && git rev-list HEAD | - while test $i -lt $num_notes && read sha1 + while test $i -lt $remove_notes && read sha1 do i=$(($i + 1)) && test_tick && - git notes remove "$sha1" || - exit 1 + git notes remove "$sha1" 2>/dev/null || return 1 done ' test_expect_success 'most notes deleted correctly with git-notes' ' - git log HEAD~250 | grep "^ " > output && - i=50 && + git log HEAD~$remove_notes | grep "^ " > output && + i=$(($num_notes - $remove_notes)) && while test $i -gt 0 do echo " commit #$i" && @@ -67,16 +105,29 @@ test_expect_success 'most notes deleted correctly with git-notes' ' test_cmp expect output ' -test_expect_success 'deleting most notes triggers fanout consolidation' ' - # Expect entire notes tree to have a fanout == 0 - git ls-tree -r --name-only refs/notes/commits | - while read path +test_expect_success 'stable fanout 1 is followed by stable fanout 0' ' + i=$remove_notes && + fanout=1 && + while test $i -gt 0 do - echo $path | grep -v "^../.*" || { - echo "Invalid path \"$path\"" && - return 1; - } - done + i=$(($i - 1)) && + if touched_one_note_with_fanout refs/notes/commits~$i D $fanout + then + continue + elif test $fanout -eq 1 + then + fanout=0 && + if all_notes_have_fanout refs/notes/commits~$i $fanout + then + echo "Fanout 1 -> 0 at refs/notes/commits~$i" && + continue + fi + fi && + echo "Failed fanout=$fanout check at refs/notes/commits~$i" && + git ls-tree -r --name-only refs/notes/commits~$i && + return 1 + done && + all_notes_have_fanout refs/notes/commits 0 ' test_done -- cgit v0.10.2-6-g49f6 From dbc27477ffb1e66f224f2e3e7d91b10c2274168e Mon Sep 17 00:00:00 2001 From: Johan Herland Date: Mon, 3 Feb 2020 22:04:45 +0100 Subject: notes.c: fix off-by-one error when decreasing notes fanout As noted in the previous commit, the nature of the fanout heuristic in the notes code causes the exact point at which we increase or decrease the notes fanout to vary with the objects being annotated. Since the object ids generated by the test environment are deterministic (by design), the notes generated and tested by t3305 are always the same, and we therefore happen to see the same fanout behavior from one run to the next. Coincidentally, if we were to change the test environment slightly (say by making a test commit on an unrelated branch before we start the t3305 test proper), we not only see the fanout switch happen at different points, we also manage to trigger a _bug_ in the notes code where the fanout 1 -> 0 switch is not applied uniformly across the notes tree, but instead yields a notes tree like this: ... bdeafb301e44b0e4db0f738a2d2a7beefdb70b70 bff2d39b4f7122bd4c5caee3de353a774d1e632a d3/8ec8f851adf470131178085bfbaab4b12ad2a7 e0b173960431a3e692ae929736df3c9b73a11d5b eb3c3aede523d729990ac25c62a93eb47c21e2e3 ... The bug occurs when we are writing out a notes tree with a newly decreased fanout, and the notes tree contains unexpanded subtrees that should be consolidated into the parent tree as a consequence of the decreased fanout): Subtrees that happen to sit at an _even_ level in the internal notes 16-tree structure (in other words: subtrees whose path - "d3" in the example above - is unique in the first nibble - i.e. there are no other note paths that start with "d") are _not_ unpacked as part of the tree writeout. This error will repeat itself in subsequent note trees until the subtree is forced to be unpacked. In t3305 this only happens when the d38ec8f8 note is itself removed from the tree. The error is not severe (no information is lost, and the notes code is able to read/decode this tree and manipulate it correctly), but this is nonetheless a bug in the current implementation that should be fixed. That said, fixing the off-by-one error is not without complications: We must take into account that the load_subtree() call from for_each_note_helper() (that is now done to correctly unpack the subtree while we're writing out the notes tree) may end up inserting unpacked non-notes into the linked list of non_note entries held by the struct notes_tree. Since we are in the process of writing out the notes tree, this linked list is currently in the process of being traversed by write_each_non_note_until(). The unpacked non-notes are necessarily inserted between the last non-note we wrote out, and the next non-note to be written. Hence, we cannot simply hold the next_non_note to write in struct write_each_note_data (as we would then silently skip these newly inserted notes), but must instead always follow the ->next pointer from the last non-note we wrote. (This part was caught by an existing test in t3304.) Cc: Johannes Schindelin Cc: Brian M. Carlson Signed-off-by: Johan Herland Signed-off-by: Junio C Hamano diff --git a/notes.c b/notes.c index 03e7d0c..009fa8a 100644 --- a/notes.c +++ b/notes.c @@ -576,16 +576,16 @@ redo: * the note tree that have not yet been explored. There * is a direct relationship between subtree entries at * level 'n' in the tree, and the 'fanout' variable: - * Subtree entries at level 'n <= 2 * fanout' should be + * Subtree entries at level 'n < 2 * fanout' should be * preserved, since they correspond exactly to a fanout * directory in the on-disk structure. However, subtree - * entries at level 'n > 2 * fanout' should NOT be + * entries at level 'n >= 2 * fanout' should NOT be * preserved, but rather consolidated into the above * notes tree level. We achieve this by unconditionally * unpacking subtree entries that exist below the * threshold level at 'n = 2 * fanout'. */ - if (n <= 2 * fanout && + if (n < 2 * fanout && flags & FOR_EACH_NOTE_YIELD_SUBTREES) { /* invoke callback with subtree */ unsigned int path_len = @@ -602,7 +602,7 @@ redo: path, cb_data); } - if (n > fanout * 2 || + if (n >= 2 * fanout || !(flags & FOR_EACH_NOTE_DONT_UNPACK_SUBTREES)) { /* unpack subtree and resume traversal */ tree->a[i] = NULL; @@ -723,13 +723,15 @@ static int write_each_note_helper(struct tree_write_stack *tws, struct write_each_note_data { struct tree_write_stack *root; - struct non_note *next_non_note; + struct non_note **nn_list; + struct non_note *nn_prev; }; static int write_each_non_note_until(const char *note_path, struct write_each_note_data *d) { - struct non_note *n = d->next_non_note; + struct non_note *p = d->nn_prev; + struct non_note *n = p ? p->next : *d->nn_list; int cmp = 0, ret; while (n && (!note_path || (cmp = strcmp(n->path, note_path)) <= 0)) { if (note_path && cmp == 0) @@ -740,9 +742,10 @@ static int write_each_non_note_until(const char *note_path, if (ret) return ret; } + p = n; n = n->next; } - d->next_non_note = n; + d->nn_prev = p; return 0; } @@ -1144,7 +1147,8 @@ int write_notes_tree(struct notes_tree *t, struct object_id *result) strbuf_init(&root.buf, 256 * (32 + the_hash_algo->hexsz)); /* assume 256 entries */ root.path[0] = root.path[1] = '\0'; cb_data.root = &root; - cb_data.next_non_note = t->first_non_note; + cb_data.nn_list = &(t->first_non_note); + cb_data.nn_prev = NULL; /* Write tree objects representing current notes tree */ flags = FOR_EACH_NOTE_DONT_UNPACK_SUBTREES | diff --git a/t/t3305-notes-fanout.sh b/t/t3305-notes-fanout.sh index 402057c..3b4753e 100755 --- a/t/t3305-notes-fanout.sh +++ b/t/t3305-notes-fanout.sh @@ -30,6 +30,12 @@ all_notes_have_fanout() { done } +test_expect_success 'tweak test environment' ' + git checkout -b nondeterminism && + test_commit A && + git checkout --orphan with_notes; +' + test_expect_success 'creating many notes with git-notes' ' num_notes=300 && i=0 && -- cgit v0.10.2-6-g49f6