diff --git a/contrib/pageinspect/expected/hash.out b/contrib/pageinspect/expected/hash.out index 3ba01f6..c97b279 100644 --- a/contrib/pageinspect/expected/hash.out +++ b/contrib/pageinspect/expected/hash.out @@ -51,13 +51,13 @@ bsize | 8152 bmsize | 4096 bmshift | 15 maxbucket | 3 -highmask | 7 -lowmask | 3 -ovflpoint | 2 +highmask | 3 +lowmask | 1 +ovflpoint | 3 firstfree | 0 nmaps | 1 procid | 450 -spares | {0,0,1,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0} +spares | {0,0,0,1,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0} mapp | {5,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0} SELECT magic, version, ntuples, bsize, bmsize, bmshift, maxbucket, highmask, diff --git a/doc/src/sgml/pageinspect.sgml b/doc/src/sgml/pageinspect.sgml index 9f41bb2..f19066f 100644 --- a/doc/src/sgml/pageinspect.sgml +++ b/doc/src/sgml/pageinspect.sgml @@ -667,11 +667,11 @@ bmshift | 15 maxbucket | 12512 highmask | 16383 lowmask | 8191 -ovflpoint | 14 +ovflpoint | 50 firstfree | 1204 nmaps | 1 procid | 450 -spares | {0,0,0,0,0,0,1,1,1,1,1,4,59,704,1204,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0} +spares | {0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,3,4,4,4,45,55,58,59,508,567,628,704,1193,1202,1204,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0} mapp | {65,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0} diff --git a/src/backend/access/hash/README b/src/backend/access/hash/README index 1541438..ff527c1 100644 --- a/src/backend/access/hash/README +++ b/src/backend/access/hash/README @@ -58,35 +58,51 @@ rules to support a variable number of overflow pages while not having to move primary bucket pages around after they are created. Primary bucket pages (henceforth just "bucket pages") are allocated in -power-of-2 groups, called "split points" in the code. Buckets 0 and 1 -are created when the index is initialized. At the first split, buckets 2 -and 3 are allocated; when bucket 4 is needed, buckets 4-7 are allocated; -when bucket 8 is needed, buckets 8-15 are allocated; etc. All the bucket -pages of a power-of-2 group appear consecutively in the index. This -addressing scheme allows the physical location of a bucket page to be -computed from the bucket number relatively easily, using only a small -amount of control information. We take the log2() of the bucket number -to determine which split point S the bucket belongs to, and then simply -add "hashm_spares[S] + 1" (where hashm_spares[] is an array stored in the -metapage) to compute the physical address. hashm_spares[S] can be -interpreted as the total number of overflow pages that have been allocated -before the bucket pages of splitpoint S. hashm_spares[0] is always 0, -so that buckets 0 and 1 (which belong to splitpoint 0) always appear at -block numbers 1 and 2, just after the meta page. We always have -hashm_spares[N] <= hashm_spares[N+1], since the latter count includes the -former. The difference between the two represents the number of overflow -pages appearing between the bucket page groups of splitpoints N and N+1. - +power-of-2 groups, called "split points" in the code. That means at every new +split point we double the existing number of buckets. Allocating huge chucks +of bucket pages all at once isn't optimal and we will take ages to consume +those. To avoid this exponential growth of index size, we did use a trick to +breakup allocation of buckets at the splitpoint into 4 equal phases. If +(2 ^ x) is the total buckets need to be allocated at a splitpoint (from now on +we shall call this as a splitpoint group), then we allocate 1/4th (2 ^ (x - 2)) +of total buckets at each phase of splitpoint group. Next quarter of allocation +will only happen if buckets of previous phase has been already consumed. Since +for buckets number < 4 we cannot further divide it in to multiple phases, the +first splitpoint group 0's allocation is done as follows {1, 1, 1, 1} = 4 +buckets in total, the numbers in curly braces indicate number of buckets +allocated within each phase of splitpoint group 0. In next splitpoint group 1 +the allocation phases will be as follow {1, 1, 1, 1} = 8 buckets in total. +And, for splitpoint group 2 and 3 allocation phase will be {2, 2, 2, 2} = 16 +buckets in total and {4, 4, 4, 4} = 32 buckets in total. We can see that at +each splitpoint group we double the total number of buckets from previous group +but in an incremental phase. The bucket pages allocated within one phase of a +splitpoint group will appear consecutively in the index. This addressing +scheme allows the physical location of a bucket page to be computed from the +bucket number relatively easily, using only a small amount of control +information. If we look at the function _hash_spareindex for a given bucket +number we first compute the splitpoint group it belongs to and then the phase +to which the bucket belongs to. Adding them we get the global splitpoint phase +number S to which the bucket belongs and then simply add "hashm_spares[S] + 1" +(where hashm_spares[] is an array stored in the metapage) with given bucket +number to compute its physical address. The hashm_spares[S] can be interpreted +as the total number of overflow pages that have been allocated before the +bucket pages of splitpoint phase S. The hashm_spares[0] is always 0, so that +buckets 0 and 1 (which belong to splitpoint group 0's phase 1 and phase 2 +respectively) always appear at block numbers 1 and 2, just after the meta page. +We always have hashm_spares[N] <= hashm_spares[N+1], since the latter count +includes the former. The difference between the two represents the number of +overflow pages appearing between the bucket page groups of splitpoints phase N +and N+1. (Note: the above describes what happens when filling an initially minimally -sized hash index. In practice, we try to estimate the required index size -and allocate a suitable number of splitpoints immediately, to avoid +sized hash index. In practice, we try to estimate the required index size and +allocate a suitable number of splitpoints phases immediately, to avoid expensive re-splitting during initial index build.) When S splitpoints exist altogether, the array entries hashm_spares[0] through hashm_spares[S] are valid; hashm_spares[S] records the current total number of overflow pages. New overflow pages are created as needed at the end of the index, and recorded by incrementing hashm_spares[S]. -When it is time to create a new splitpoint's worth of bucket pages, we +When it is time to create a new splitpoint phase's worth of bucket pages, we copy hashm_spares[S] into hashm_spares[S+1] and increment S (which is stored in the hashm_ovflpoint field of the meta page). This has the effect of reserving the correct number of bucket pages at the end of the @@ -101,7 +117,7 @@ We have to allow the case "greater than" because it's possible that during an index extension we crash after allocating filesystem space and before updating the metapage. Note that on filesystems that allow "holes" in files, it's entirely likely that pages before the logical EOF are not yet -allocated: when we allocate a new splitpoint's worth of bucket pages, we +allocated: when we allocate a new splitpoint phase's worth of bucket pages, we physically zero the last such page to force the EOF up, and the first such page will be used immediately, but the intervening pages are not written until needed. diff --git a/src/backend/access/hash/hashovfl.c b/src/backend/access/hash/hashovfl.c index a3cae21..fe0b4ef 100644 --- a/src/backend/access/hash/hashovfl.c +++ b/src/backend/access/hash/hashovfl.c @@ -49,7 +49,7 @@ bitno_to_blkno(HashMetaPage metap, uint32 ovflbitnum) * Convert to absolute page number by adding the number of bucket pages * that exist before this split point. */ - return (BlockNumber) ((1 << i) + ovflbitnum); + return (BlockNumber) (_hash_get_totalbuckets(i) + ovflbitnum); } /* @@ -67,14 +67,15 @@ _hash_ovflblkno_to_bitno(HashMetaPage metap, BlockNumber ovflblkno) /* Determine the split number containing this page */ for (i = 1; i <= splitnum; i++) { - if (ovflblkno <= (BlockNumber) (1 << i)) + if (ovflblkno <= (BlockNumber) _hash_get_totalbuckets(i)) break; /* oops */ - bitnum = ovflblkno - (1 << i); + bitnum = ovflblkno - _hash_get_totalbuckets(i); /* * bitnum has to be greater than number of overflow page added in * previous split point. The overflow page at this splitnum (i) if any - * should start from ((2 ^ i) + metap->hashm_spares[i - 1] + 1). + * should start from + * (_hash_get_totalbuckets(i) + metap->hashm_spares[i - 1] + 1). */ if (bitnum > metap->hashm_spares[i - 1] && bitnum <= metap->hashm_spares[i]) diff --git a/src/backend/access/hash/hashpage.c b/src/backend/access/hash/hashpage.c index 61ca2ec..b8d682f 100644 --- a/src/backend/access/hash/hashpage.c +++ b/src/backend/access/hash/hashpage.c @@ -502,14 +502,15 @@ _hash_init_metabuffer(Buffer buf, double num_tuples, RegProcedure procid, Page page; double dnumbuckets; uint32 num_buckets; - uint32 log2_num_buckets; + uint32 spare_index; uint32 i; /* * Choose the number of initial bucket pages to match the fill factor * given the estimated number of tuples. We round up the result to the - * next power of 2, however, and always force at least 2 bucket pages. The - * upper limit is determined by considerations explained in + * total number of buckets which has to be allocated before using its + * _hashm_spares index slot. However always force at least 2 bucket pages. + * The upper limit is determined by considerations explained in * _hash_expandtable(). */ dnumbuckets = num_tuples / ffactor; @@ -518,11 +519,10 @@ _hash_init_metabuffer(Buffer buf, double num_tuples, RegProcedure procid, else if (dnumbuckets >= (double) 0x40000000) num_buckets = 0x40000000; else - num_buckets = ((uint32) 1) << _hash_log2((uint32) dnumbuckets); + num_buckets = _hash_get_totalbuckets(_hash_spareindex(dnumbuckets)); - log2_num_buckets = _hash_log2(num_buckets); - Assert(num_buckets == (((uint32) 1) << log2_num_buckets)); - Assert(log2_num_buckets < HASH_MAX_SPLITPOINTS); + spare_index = _hash_spareindex(num_buckets); + Assert(spare_index < HASH_MAX_SPLITPOINTS); page = BufferGetPage(buf); if (initpage) @@ -563,18 +563,20 @@ _hash_init_metabuffer(Buffer buf, double num_tuples, RegProcedure procid, /* * We initialize the index with N buckets, 0 .. N-1, occupying physical - * blocks 1 to N. The first freespace bitmap page is in block N+1. Since - * N is a power of 2, we can set the masks this way: + * blocks 1 to N. The first freespace bitmap page is in block N+1. */ - metap->hashm_maxbucket = metap->hashm_lowmask = num_buckets - 1; - metap->hashm_highmask = (num_buckets << 1) - 1; + metap->hashm_maxbucket = num_buckets - 1; + + /* set highmask, which should be sufficient to cover num_buckets. */ + metap->hashm_highmask = (1 << (_hash_log2(num_buckets))) - 1; + metap->hashm_lowmask = (metap->hashm_highmask >> 1); MemSet(metap->hashm_spares, 0, sizeof(metap->hashm_spares)); MemSet(metap->hashm_mapp, 0, sizeof(metap->hashm_mapp)); /* Set up mapping for one spare page after the initial splitpoints */ - metap->hashm_spares[log2_num_buckets] = 1; - metap->hashm_ovflpoint = log2_num_buckets; + metap->hashm_spares[spare_index] = 1; + metap->hashm_ovflpoint = spare_index; metap->hashm_firstfree = 0; /* @@ -773,25 +775,40 @@ restart_expand: start_nblkno = BUCKET_TO_BLKNO(metap, new_bucket); /* - * If the split point is increasing (hashm_maxbucket's log base 2 - * increases), we need to allocate a new batch of bucket pages. + * If the split point is increasing we need to allocate a new batch of + * bucket pages. */ - spare_ndx = _hash_log2(new_bucket + 1); + spare_ndx = _hash_spareindex(new_bucket + 1); if (spare_ndx > metap->hashm_ovflpoint) { + uint32 buckets_toadd = 0; + uint32 splitpoint_group = 0; + Assert(spare_ndx == metap->hashm_ovflpoint + 1); /* - * The number of buckets in the new splitpoint is equal to the total - * number already in existence, i.e. new_bucket. Currently this maps - * one-to-one to blocks required, but someday we may need a more - * complicated calculation here. We treat allocation of buckets as a - * separate WAL-logged action. Even if we fail after this operation, + * The number of buckets in the new splitpoint group is equal to the + * total number already in existence, i.e. new_bucket. But we do not + * allocate them at once. Each splitpoint group will have 4 slots, we + * distribute the buckets equally among them. So we allocate only one + * fourth of total buckets in new splitpoint group at a time to consume + * one phase after another. We treat allocation of buckets as a + * separate WAL-logged action. Even if we fail after this operation, * won't leak bucket pages; rather, the next split will consume this * space. In any case, even without failure we don't use all the space * in one split operation. */ - if (!_hash_alloc_buckets(rel, start_nblkno, new_bucket)) + splitpoint_group = (spare_ndx >> 2); + + /* + * Each phase in the splitpoint_group will allocate + * 2^(splitpoint_group - 1) buckets if we divide buckets among 4 + * slots. The 0th group is a special case where we allocate 1 bucket + * per slot as we cannot reduce it any further. See README for more + * details. + */ + buckets_toadd = (splitpoint_group) ? (1 << (splitpoint_group - 1)) : 1; + if (!_hash_alloc_buckets(rel, start_nblkno, buckets_toadd)) { /* can't split due to BlockNumber overflow */ _hash_relbuf(rel, buf_oblkno); @@ -836,10 +853,9 @@ restart_expand: } /* - * If the split point is increasing (hashm_maxbucket's log base 2 - * increases), we need to adjust the hashm_spares[] array and - * hashm_ovflpoint so that future overflow pages will be created beyond - * this new batch of bucket pages. + * If the split point is increasing we need to adjust the hashm_spares[] + * array and hashm_ovflpoint so that future overflow pages will be created + * beyond this new batch of bucket pages. */ if (spare_ndx > metap->hashm_ovflpoint) { diff --git a/src/backend/access/hash/hashutil.c b/src/backend/access/hash/hashutil.c index 2e99719..98975e1 100644 --- a/src/backend/access/hash/hashutil.c +++ b/src/backend/access/hash/hashutil.c @@ -149,6 +149,84 @@ _hash_log2(uint32 num) return i; } +#define SPLITPOINT_PHASES_PER_GRP 4 +#define SPLITPOINT_PHASE_MASK (SPLITPOINT_PHASES_PER_GRP - 1) +#define Buckets_First_Split_Group 4 + +#define TOTAL_SPLITPOINT_PHASES_BEFORE_GROUP(sp_g) (sp_g > 0 ? (sp_g << 2) : 0) + +/* + * This is just a trick to save a division operation. If you look into the + * bitmap of 0-based bucket_num 2nd and 3rd most significant bit will indicate + * which phase of allocation the bucket_num belongs to with in the group. This + * is because at every splitpoint group we allocate (2 ^ x) buckets and we have + * divided the allocation process into 4 equal phases. This macro returns value + * from 0 to 3. + */ +#define SPLITPOINT_PHASES_WITHIN_GROUP(sp_g, bucket_num) \ + ((sp_g > 0) ? (((bucket_num) >> (sp_g - 1)) & SPLITPOINT_PHASE_MASK) : \ + (bucket_num)) + +/* + * At splitpoint group 0 we have 2 ^ (0 + 2) = 4 buckets, then at splitpoint + * group 1 we have 2 ^ (1 + 2) = 8 total buckets. As the doubling continues at + * splitpoint group "x" we will have 2 ^ (x + 2) total buckets. Total buckets + * before x splitpoint group will be 2 ^ (x + 1). At each phase of allocation + * within splitpoint group we add 2 ^ (x - 1) buckets, as we have to divide the + * task of allocation of 2 ^ (x + 1) buckets among 4 phases. + * + * Also, splitpoint group of a given bucket can be taken as + * (_hash_log2(bucket) - 2). Subtracted by 2 because each group have + * 2 ^ (x + 2) buckets. + */ +#define BUCKETS_BEFORE_SP_GRP(sp_g) ((sp_g == 0) ? 0 : (1 << (sp_g + 1))) +#define BUCKETS_WITHIN_SP_GRP(sp_g, nphase) \ + ((nphase) * ((sp_g == 0) ? 1 : (1 << (sp_g - 1)))) +#define BUCKET_TO_SPLITPOINT_GRP(num_bucket) \ + ((num_bucket <= Buckets_First_Split_Group) ? 0 : \ + (_hash_log2(num_bucket) - 2)) + +/* + * _hash_spareindex -- returns spare index / global splitpoint phase of the + * bucket + */ +uint32 +_hash_spareindex(uint32 num_bucket) +{ + uint32 splitpoint_group; + + splitpoint_group = BUCKET_TO_SPLITPOINT_GRP(num_bucket); + + return TOTAL_SPLITPOINT_PHASES_BEFORE_GROUP(splitpoint_group) + + SPLITPOINT_PHASES_WITHIN_GROUP(splitpoint_group, + num_bucket - 1); /* make it 0-based */ +} + +/* + * _hash_get_totalbuckets -- returns total number of buckets allocated till + * the given splitpoint phase. + */ +uint32 +_hash_get_totalbuckets(uint32 splitpoint_phase) +{ + uint32 splitpoint_group; + + /* + * Every 4 consecutive phases makes one group and group's are numbered + * from 0 + */ + splitpoint_group = (splitpoint_phase / SPLITPOINT_PHASES_PER_GRP); + + /* + * total_buckets = total number of buckets before its splitpoint group + + * total buckets within its splitpoint group until given splitpoint_phase. + */ + return BUCKETS_BEFORE_SP_GRP(splitpoint_group) + + BUCKETS_WITHIN_SP_GRP(splitpoint_group, + (splitpoint_phase % SPLITPOINT_PHASES_PER_GRP) + + 1); +} + /* * _hash_checkpage -- sanity checks on the format of all hash pages * diff --git a/src/include/access/hash.h b/src/include/access/hash.h index eb1df57..ac502ef 100644 --- a/src/include/access/hash.h +++ b/src/include/access/hash.h @@ -36,7 +36,7 @@ typedef uint32 Bucket; #define InvalidBucket ((Bucket) 0xFFFFFFFF) #define BUCKET_TO_BLKNO(metap,B) \ - ((BlockNumber) ((B) + ((B) ? (metap)->hashm_spares[_hash_log2((B)+1)-1] : 0)) + 1) + ((BlockNumber) ((B) + ((B) ? (metap)->hashm_spares[_hash_spareindex((B)+1)-1] : 0)) + 1) /* * Special space for hash index pages. @@ -180,7 +180,7 @@ typedef HashScanOpaqueData *HashScanOpaque; * needing to fit into the metapage. (With 8K block size, 128 bitmaps * limit us to 64 GB of overflow space...) */ -#define HASH_MAX_SPLITPOINTS 32 +#define HASH_MAX_SPLITPOINTS 128 #define HASH_MAX_BITMAPS 128 typedef struct HashMetaPageData @@ -382,6 +382,8 @@ extern uint32 _hash_datum2hashkey_type(Relation rel, Datum key, Oid keytype); extern Bucket _hash_hashkey2bucket(uint32 hashkey, uint32 maxbucket, uint32 highmask, uint32 lowmask); extern uint32 _hash_log2(uint32 num); +extern uint32 _hash_spareindex(uint32 num_bucket); +extern uint32 _hash_get_totalbuckets(uint32 splitpoint_phase); extern void _hash_checkpage(Relation rel, Buffer buf, int flags); extern uint32 _hash_get_indextuple_hashkey(IndexTuple itup); extern bool _hash_convert_tuple(Relation index,