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comparison tests/test-sparse-revlog.t @ 39493:3ca144f1c8dd

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snapshot: search for unrelated but reusable full-snapshot # New Strategy Step: Reusing Snapshot Outside Of Parents' Chain. If no suitable bases were found in the parent's chains, see if we could reuse a full snapshot not directly related to the current revision. Such search can be expensive, so we only search for snapshots appended to the revlog *after* the bases used by the parents of the current revision (the one we just tested). We assume the parent's bases were created because the previous snapshots were unsuitable, so there are low odds they would be useful now. This search gives a chance to reuse a delta chain unrelated to the current revision. Without this re-use, topological branches would keep reopening new full chains. Creating more and more snapshots as the repository grow. In repositories with many topological branches, the lack of delta reuse can create too many snapshots reducing overall compression to nothing. This results in a very large repository and other usability issues. For now, we still focus on creating level-1 snapshots. However, this principle will play a large part in how we avoid snapshot explosion once we have more snapshot levels. # Effects On The Test Repository In the test repository we created, we can see the beneficial effect of such reuse. We need very few level-0 snapshots and the overall revlog size has decreased. The `hg debugrevlog` call, show a "lvl-2" snapshot. It comes from the existing delta logic using the `prev` revision (revlog's tip) as the base. In this specific case, it turns out the tip was a level-1 snapshot. This is a coincidence that can be ignored. Finding and testing against all these unrelated snapshots can have a performance impact at write time. We currently focus on building good deltas chain we build. Performance concern will be dealt with later in another series.
author Boris Feld <boris.feld@octobus.net>
date Fri, 07 Sep 2018 11:17:30 -0400
parents a33f394b2bfd
children e72130f58f5d
comparison
equal deleted inserted replaced
39492:a33f394b2bfd 39493:3ca144f1c8dd
75 SPARSE-REVLOG-TEST-FILE | 1068 +++++++++++++++++++++++----------------------- 75 SPARSE-REVLOG-TEST-FILE | 1068 +++++++++++++++++++++++-----------------------
76 1 files changed, 534 insertions(+), 534 deletions(-) 76 1 files changed, 534 insertions(+), 534 deletions(-)
77 77
78 78
79 $ f -s .hg/store/data/*.d 79 $ f -s .hg/store/data/*.d
80 .hg/store/data/_s_p_a_r_s_e-_r_e_v_l_o_g-_t_e_s_t-_f_i_l_e.d: size=72315280 80 .hg/store/data/_s_p_a_r_s_e-_r_e_v_l_o_g-_t_e_s_t-_f_i_l_e.d: size=67810463
81 $ hg debugrevlog * 81 $ hg debugrevlog *
82 format : 1 82 format : 1
83 flags : generaldelta 83 flags : generaldelta
84 84
85 revisions : 5001 85 revisions : 5001
87 normal : 4376 (87.50%) 87 normal : 4376 (87.50%)
88 revisions : 5001 88 revisions : 5001
89 empty : 0 ( 0.00%) 89 empty : 0 ( 0.00%)
90 text : 0 (100.00%) 90 text : 0 (100.00%)
91 delta : 0 (100.00%) 91 delta : 0 (100.00%)
92 snapshot : 145 ( 2.90%) 92 snapshot : 126 ( 2.52%)
93 lvl-0 : 15 ( 0.30%) 93 lvl-0 : 4 ( 0.08%)
94 lvl-1 : 130 ( 2.60%) 94 lvl-1 : 120 ( 2.40%)
95 deltas : 4856 (97.10%) 95 lvl-2 : 2 ( 0.04%)
96 revision size : 72315280 96 deltas : 4875 (97.48%)
97 snapshot : 18481085 (25.56%) 97 revision size : 67810463
98 lvl-0 : 3016019 ( 4.17%) 98 snapshot : 14373347 (21.20%)
99 lvl-1 : 15465066 (21.39%) 99 lvl-0 : 804235 ( 1.19%)
100 deltas : 53834195 (74.44%) 100 lvl-1 : 13535903 (19.96%)
101 lvl-2 : 33209 ( 0.05%)
102 deltas : 53437116 (78.80%)
101 103
102 chunks : 5001 104 chunks : 5001
103 0x78 (x) : 5001 (100.00%) 105 0x78 (x) : 5001 (100.00%)
104 chunks size : 72315280 106 chunks size : 67810463
105 0x78 (x) : 72315280 (100.00%) 107 0x78 (x) : 67810463 (100.00%)
106 108
107 avg chain length : 18 109 avg chain length : 18
108 max chain length : 45 110 max chain length : 45
109 max chain reach : 32095083 111 max chain reach : 25808240
110 compression ratio : 23 112 compression ratio : 25
111 113
112 uncompressed data size (min/max/avg) : 346468 / 346472 / 346471 114 uncompressed data size (min/max/avg) : 346468 / 346472 / 346471
113 full revision size (min/max/avg) : 200990 / 201151 / 201067 115 full revision size (min/max/avg) : 201014 / 201116 / 201058
114 inter-snapshot size (min/max/avg) : 37202 / 173034 / 118962 116 inter-snapshot size (min/max/avg) : 11623 / 173150 / 111222
115 level-1 (min/max/avg) : 37202 / 173034 / 118962 117 level-1 (min/max/avg) : 11623 / 173150 / 112799
116 delta size (min/max/avg) : 10649 / 104791 / 11086 118 level-2 (min/max/avg) : 14151 / 19058 / 16604
119 delta size (min/max/avg) : 10649 / 101790 / 10961
117 120
118 deltas against prev : 4185 (86.18%) 121 deltas against prev : 4207 (86.30%)
119 where prev = p1 : 4139 (98.90%) 122 where prev = p1 : 4164 (98.98%)
120 where prev = p2 : 0 ( 0.00%) 123 where prev = p2 : 0 ( 0.00%)
121 other : 46 ( 1.10%) 124 other : 43 ( 1.02%)
122 deltas against p1 : 647 (13.32%) 125 deltas against p1 : 653 (13.39%)
123 deltas against p2 : 24 ( 0.49%) 126 deltas against p2 : 15 ( 0.31%)
124 deltas against other : 0 ( 0.00%) 127 deltas against other : 0 ( 0.00%)