sslobodr | d046be8 | 2019-01-16 10:02:22 -0500 | [diff] [blame^] | 1 | package bolt |
| 2 | |
| 3 | import ( |
| 4 | "fmt" |
| 5 | "sort" |
| 6 | "unsafe" |
| 7 | ) |
| 8 | |
| 9 | // freelist represents a list of all pages that are available for allocation. |
| 10 | // It also tracks pages that have been freed but are still in use by open transactions. |
| 11 | type freelist struct { |
| 12 | ids []pgid // all free and available free page ids. |
| 13 | pending map[txid][]pgid // mapping of soon-to-be free page ids by tx. |
| 14 | cache map[pgid]bool // fast lookup of all free and pending page ids. |
| 15 | } |
| 16 | |
| 17 | // newFreelist returns an empty, initialized freelist. |
| 18 | func newFreelist() *freelist { |
| 19 | return &freelist{ |
| 20 | pending: make(map[txid][]pgid), |
| 21 | cache: make(map[pgid]bool), |
| 22 | } |
| 23 | } |
| 24 | |
| 25 | // size returns the size of the page after serialization. |
| 26 | func (f *freelist) size() int { |
| 27 | return pageHeaderSize + (int(unsafe.Sizeof(pgid(0))) * f.count()) |
| 28 | } |
| 29 | |
| 30 | // count returns count of pages on the freelist |
| 31 | func (f *freelist) count() int { |
| 32 | return f.free_count() + f.pending_count() |
| 33 | } |
| 34 | |
| 35 | // free_count returns count of free pages |
| 36 | func (f *freelist) free_count() int { |
| 37 | return len(f.ids) |
| 38 | } |
| 39 | |
| 40 | // pending_count returns count of pending pages |
| 41 | func (f *freelist) pending_count() int { |
| 42 | var count int |
| 43 | for _, list := range f.pending { |
| 44 | count += len(list) |
| 45 | } |
| 46 | return count |
| 47 | } |
| 48 | |
| 49 | // all returns a list of all free ids and all pending ids in one sorted list. |
| 50 | func (f *freelist) all() []pgid { |
| 51 | m := make(pgids, 0) |
| 52 | |
| 53 | for _, list := range f.pending { |
| 54 | m = append(m, list...) |
| 55 | } |
| 56 | |
| 57 | sort.Sort(m) |
| 58 | return pgids(f.ids).merge(m) |
| 59 | } |
| 60 | |
| 61 | // allocate returns the starting page id of a contiguous list of pages of a given size. |
| 62 | // If a contiguous block cannot be found then 0 is returned. |
| 63 | func (f *freelist) allocate(n int) pgid { |
| 64 | if len(f.ids) == 0 { |
| 65 | return 0 |
| 66 | } |
| 67 | |
| 68 | var initial, previd pgid |
| 69 | for i, id := range f.ids { |
| 70 | if id <= 1 { |
| 71 | panic(fmt.Sprintf("invalid page allocation: %d", id)) |
| 72 | } |
| 73 | |
| 74 | // Reset initial page if this is not contiguous. |
| 75 | if previd == 0 || id-previd != 1 { |
| 76 | initial = id |
| 77 | } |
| 78 | |
| 79 | // If we found a contiguous block then remove it and return it. |
| 80 | if (id-initial)+1 == pgid(n) { |
| 81 | // If we're allocating off the beginning then take the fast path |
| 82 | // and just adjust the existing slice. This will use extra memory |
| 83 | // temporarily but the append() in free() will realloc the slice |
| 84 | // as is necessary. |
| 85 | if (i + 1) == n { |
| 86 | f.ids = f.ids[i+1:] |
| 87 | } else { |
| 88 | copy(f.ids[i-n+1:], f.ids[i+1:]) |
| 89 | f.ids = f.ids[:len(f.ids)-n] |
| 90 | } |
| 91 | |
| 92 | // Remove from the free cache. |
| 93 | for i := pgid(0); i < pgid(n); i++ { |
| 94 | delete(f.cache, initial+i) |
| 95 | } |
| 96 | |
| 97 | return initial |
| 98 | } |
| 99 | |
| 100 | previd = id |
| 101 | } |
| 102 | return 0 |
| 103 | } |
| 104 | |
| 105 | // free releases a page and its overflow for a given transaction id. |
| 106 | // If the page is already free then a panic will occur. |
| 107 | func (f *freelist) free(txid txid, p *page) { |
| 108 | if p.id <= 1 { |
| 109 | panic(fmt.Sprintf("cannot free page 0 or 1: %d", p.id)) |
| 110 | } |
| 111 | |
| 112 | // Free page and all its overflow pages. |
| 113 | var ids = f.pending[txid] |
| 114 | for id := p.id; id <= p.id+pgid(p.overflow); id++ { |
| 115 | // Verify that page is not already free. |
| 116 | if f.cache[id] { |
| 117 | panic(fmt.Sprintf("page %d already freed", id)) |
| 118 | } |
| 119 | |
| 120 | // Add to the freelist and cache. |
| 121 | ids = append(ids, id) |
| 122 | f.cache[id] = true |
| 123 | } |
| 124 | f.pending[txid] = ids |
| 125 | } |
| 126 | |
| 127 | // release moves all page ids for a transaction id (or older) to the freelist. |
| 128 | func (f *freelist) release(txid txid) { |
| 129 | m := make(pgids, 0) |
| 130 | for tid, ids := range f.pending { |
| 131 | if tid <= txid { |
| 132 | // Move transaction's pending pages to the available freelist. |
| 133 | // Don't remove from the cache since the page is still free. |
| 134 | m = append(m, ids...) |
| 135 | delete(f.pending, tid) |
| 136 | } |
| 137 | } |
| 138 | sort.Sort(m) |
| 139 | f.ids = pgids(f.ids).merge(m) |
| 140 | } |
| 141 | |
| 142 | // rollback removes the pages from a given pending tx. |
| 143 | func (f *freelist) rollback(txid txid) { |
| 144 | // Remove page ids from cache. |
| 145 | for _, id := range f.pending[txid] { |
| 146 | delete(f.cache, id) |
| 147 | } |
| 148 | |
| 149 | // Remove pages from pending list. |
| 150 | delete(f.pending, txid) |
| 151 | } |
| 152 | |
| 153 | // freed returns whether a given page is in the free list. |
| 154 | func (f *freelist) freed(pgid pgid) bool { |
| 155 | return f.cache[pgid] |
| 156 | } |
| 157 | |
| 158 | // read initializes the freelist from a freelist page. |
| 159 | func (f *freelist) read(p *page) { |
| 160 | // If the page.count is at the max uint16 value (64k) then it's considered |
| 161 | // an overflow and the size of the freelist is stored as the first element. |
| 162 | idx, count := 0, int(p.count) |
| 163 | if count == 0xFFFF { |
| 164 | idx = 1 |
| 165 | count = int(((*[maxAllocSize]pgid)(unsafe.Pointer(&p.ptr)))[0]) |
| 166 | } |
| 167 | |
| 168 | // Copy the list of page ids from the freelist. |
| 169 | if count == 0 { |
| 170 | f.ids = nil |
| 171 | } else { |
| 172 | ids := ((*[maxAllocSize]pgid)(unsafe.Pointer(&p.ptr)))[idx:count] |
| 173 | f.ids = make([]pgid, len(ids)) |
| 174 | copy(f.ids, ids) |
| 175 | |
| 176 | // Make sure they're sorted. |
| 177 | sort.Sort(pgids(f.ids)) |
| 178 | } |
| 179 | |
| 180 | // Rebuild the page cache. |
| 181 | f.reindex() |
| 182 | } |
| 183 | |
| 184 | // write writes the page ids onto a freelist page. All free and pending ids are |
| 185 | // saved to disk since in the event of a program crash, all pending ids will |
| 186 | // become free. |
| 187 | func (f *freelist) write(p *page) error { |
| 188 | // Combine the old free pgids and pgids waiting on an open transaction. |
| 189 | ids := f.all() |
| 190 | |
| 191 | // Update the header flag. |
| 192 | p.flags |= freelistPageFlag |
| 193 | |
| 194 | // The page.count can only hold up to 64k elements so if we overflow that |
| 195 | // number then we handle it by putting the size in the first element. |
| 196 | if len(ids) == 0 { |
| 197 | p.count = uint16(len(ids)) |
| 198 | } else if len(ids) < 0xFFFF { |
| 199 | p.count = uint16(len(ids)) |
| 200 | copy(((*[maxAllocSize]pgid)(unsafe.Pointer(&p.ptr)))[:], ids) |
| 201 | } else { |
| 202 | p.count = 0xFFFF |
| 203 | ((*[maxAllocSize]pgid)(unsafe.Pointer(&p.ptr)))[0] = pgid(len(ids)) |
| 204 | copy(((*[maxAllocSize]pgid)(unsafe.Pointer(&p.ptr)))[1:], ids) |
| 205 | } |
| 206 | |
| 207 | return nil |
| 208 | } |
| 209 | |
| 210 | // reload reads the freelist from a page and filters out pending items. |
| 211 | func (f *freelist) reload(p *page) { |
| 212 | f.read(p) |
| 213 | |
| 214 | // Build a cache of only pending pages. |
| 215 | pcache := make(map[pgid]bool) |
| 216 | for _, pendingIDs := range f.pending { |
| 217 | for _, pendingID := range pendingIDs { |
| 218 | pcache[pendingID] = true |
| 219 | } |
| 220 | } |
| 221 | |
| 222 | // Check each page in the freelist and build a new available freelist |
| 223 | // with any pages not in the pending lists. |
| 224 | var a []pgid |
| 225 | for _, id := range f.ids { |
| 226 | if !pcache[id] { |
| 227 | a = append(a, id) |
| 228 | } |
| 229 | } |
| 230 | f.ids = a |
| 231 | |
| 232 | // Once the available list is rebuilt then rebuild the free cache so that |
| 233 | // it includes the available and pending free pages. |
| 234 | f.reindex() |
| 235 | } |
| 236 | |
| 237 | // reindex rebuilds the free cache based on available and pending free lists. |
| 238 | func (f *freelist) reindex() { |
| 239 | f.cache = make(map[pgid]bool) |
| 240 | for _, id := range f.ids { |
| 241 | f.cache[id] = true |
| 242 | } |
| 243 | for _, pendingIDs := range f.pending { |
| 244 | for _, pendingID := range pendingIDs { |
| 245 | f.cache[pendingID] = true |
| 246 | } |
| 247 | } |
| 248 | } |