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#!/bin/sh
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test_description='avoid rewriting packed-refs unnecessarily'
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. ./test-lib.sh
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# Add an identifying mark to the packed-refs file header line. This
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# shouldn't upset readers, and it should be omitted if the file is
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# ever rewritten.
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mark_packed_refs () {
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sed -e "s/^\(#.*\)/\1 t1409 /" .git/packed-refs >.git/packed-refs.new &&
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mv .git/packed-refs.new .git/packed-refs
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}
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# Verify that the packed-refs file is still marked.
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check_packed_refs_marked () {
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grep -q '^#.* t1409 ' .git/packed-refs
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}
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test_expect_success 'setup' '
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git commit --allow-empty -m "Commit A" &&
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A=$(git rev-parse HEAD) &&
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git commit --allow-empty -m "Commit B" &&
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B=$(git rev-parse HEAD) &&
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git commit --allow-empty -m "Commit C" &&
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C=$(git rev-parse HEAD)
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'
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files-backend: don't rewrite the `packed-refs` file unnecessarily
Even when we are deleting references, we needn't overwrite the
`packed-refs` file if the references that we are deleting only exist
as loose references. Implement this optimization as follows:
* Add a function `is_packed_transaction_needed()`, which checks
whether a given packed-refs transaction actually needs to be carried
out (i.e., it returns false if the transaction obviously wouldn't
have any effect). This function must be called while holding the
`packed-refs` lock to avoid races.
* Change `files_transaction_prepare()` to check whether the
packed-refs transaction is actually needed. If not, squelch it, but
continue holding the `packed-refs` lock until the end of the
transaction to avoid races.
This fixes a mild regression caused by dc39e09942 (files_ref_store:
use a transaction to update packed refs, 2017-09-08). Before that
commit, unnecessary rewrites of `packed-refs` were suppressed by
`repack_without_refs()`. But the transaction-based writing introduced
by that commit didn't perform that optimization.
Note that the pre-dc39e09942 code still had to *read* the whole
`packed-refs` file to determine that the rewrite could be skipped, so
the performance for the cases that the write could be elided was
`O(N)` in the number of packed references both before and after
dc39e09942. But after that commit the constant factor increased.
This commit reimplements the optimization of eliding unnecessary
`packed-refs` rewrites. That, plus the fact that since
cfa2e29c34 (packed_ref_store: get rid of the `ref_cache` entirely,
2017-03-17) we don't necessarily have to read the whole `packed-refs`
file at all, means that deletes of one or a few loose references can
now be done with `O(n lg N)` effort, where `n` is the number of loose
references being deleted and `N` is the total number of packed
references.
This commit fixes two tests in t1409.
Signed-off-by: Michael Haggerty <mhagger@alum.mit.edu>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
7 years ago
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test_expect_success 'do not create packed-refs file gratuitously' '
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test_path_is_missing .git/packed-refs &&
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git update-ref refs/heads/foo $A &&
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test_path_is_missing .git/packed-refs &&
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git update-ref refs/heads/foo $B &&
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test_path_is_missing .git/packed-refs &&
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git update-ref refs/heads/foo $C $B &&
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test_path_is_missing .git/packed-refs &&
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git update-ref -d refs/heads/foo &&
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test_path_is_missing .git/packed-refs
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'
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test_expect_success 'check that marking the packed-refs file works' '
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git for-each-ref >expected &&
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git pack-refs --all &&
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mark_packed_refs &&
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check_packed_refs_marked &&
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git for-each-ref >actual &&
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test_cmp expected actual &&
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git pack-refs --all &&
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! check_packed_refs_marked &&
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git for-each-ref >actual2 &&
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test_cmp expected actual2
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'
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test_expect_success 'leave packed-refs untouched on update of packed' '
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git update-ref refs/heads/packed-update $A &&
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git pack-refs --all &&
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mark_packed_refs &&
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git update-ref refs/heads/packed-update $B &&
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check_packed_refs_marked
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'
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test_expect_success 'leave packed-refs untouched on checked update of packed' '
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git update-ref refs/heads/packed-checked-update $A &&
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git pack-refs --all &&
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mark_packed_refs &&
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git update-ref refs/heads/packed-checked-update $B $A &&
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check_packed_refs_marked
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'
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test_expect_success 'leave packed-refs untouched on verify of packed' '
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git update-ref refs/heads/packed-verify $A &&
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git pack-refs --all &&
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mark_packed_refs &&
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echo "verify refs/heads/packed-verify $A" | git update-ref --stdin &&
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check_packed_refs_marked
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'
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test_expect_success 'touch packed-refs on delete of packed' '
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git update-ref refs/heads/packed-delete $A &&
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git pack-refs --all &&
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mark_packed_refs &&
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git update-ref -d refs/heads/packed-delete &&
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! check_packed_refs_marked
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'
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test_expect_success 'leave packed-refs untouched on update of loose' '
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git pack-refs --all &&
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git update-ref refs/heads/loose-update $A &&
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mark_packed_refs &&
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git update-ref refs/heads/loose-update $B &&
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check_packed_refs_marked
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'
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test_expect_success 'leave packed-refs untouched on checked update of loose' '
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git pack-refs --all &&
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git update-ref refs/heads/loose-checked-update $A &&
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mark_packed_refs &&
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git update-ref refs/heads/loose-checked-update $B $A &&
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check_packed_refs_marked
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'
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test_expect_success 'leave packed-refs untouched on verify of loose' '
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git pack-refs --all &&
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git update-ref refs/heads/loose-verify $A &&
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mark_packed_refs &&
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echo "verify refs/heads/loose-verify $A" | git update-ref --stdin &&
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check_packed_refs_marked
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'
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files-backend: don't rewrite the `packed-refs` file unnecessarily
Even when we are deleting references, we needn't overwrite the
`packed-refs` file if the references that we are deleting only exist
as loose references. Implement this optimization as follows:
* Add a function `is_packed_transaction_needed()`, which checks
whether a given packed-refs transaction actually needs to be carried
out (i.e., it returns false if the transaction obviously wouldn't
have any effect). This function must be called while holding the
`packed-refs` lock to avoid races.
* Change `files_transaction_prepare()` to check whether the
packed-refs transaction is actually needed. If not, squelch it, but
continue holding the `packed-refs` lock until the end of the
transaction to avoid races.
This fixes a mild regression caused by dc39e09942 (files_ref_store:
use a transaction to update packed refs, 2017-09-08). Before that
commit, unnecessary rewrites of `packed-refs` were suppressed by
`repack_without_refs()`. But the transaction-based writing introduced
by that commit didn't perform that optimization.
Note that the pre-dc39e09942 code still had to *read* the whole
`packed-refs` file to determine that the rewrite could be skipped, so
the performance for the cases that the write could be elided was
`O(N)` in the number of packed references both before and after
dc39e09942. But after that commit the constant factor increased.
This commit reimplements the optimization of eliding unnecessary
`packed-refs` rewrites. That, plus the fact that since
cfa2e29c34 (packed_ref_store: get rid of the `ref_cache` entirely,
2017-03-17) we don't necessarily have to read the whole `packed-refs`
file at all, means that deletes of one or a few loose references can
now be done with `O(n lg N)` effort, where `n` is the number of loose
references being deleted and `N` is the total number of packed
references.
This commit fixes two tests in t1409.
Signed-off-by: Michael Haggerty <mhagger@alum.mit.edu>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
7 years ago
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test_expect_success 'leave packed-refs untouched on delete of loose' '
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git pack-refs --all &&
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git update-ref refs/heads/loose-delete $A &&
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mark_packed_refs &&
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git update-ref -d refs/heads/loose-delete &&
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check_packed_refs_marked
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'
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test_done
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