new

src/libndb/ndbhash.c

@@ -0,0 +1,247 @@
+#include <u.h>
+#include <libc.h>
+#include <bio.h>
+#include "ndb.h"
+#include "ndbhf.h"
+
+enum {
+	Dptr,	/* pointer to database file */
+	Cptr,	/* pointer to first chain entry */
+	Cptr1,	/* pointer to second chain entry */
+};
+
+/*
+ *  generate a hash value for an ascii string (val) given
+ *  a hash table length (hlen)
+ */
+ulong
+ndbhash(char *vp, int hlen)
+{
+	ulong hash;
+	uchar *val = (uchar*)vp;
+
+	for(hash = 0; *val; val++)
+		hash = (hash*13) + *val-'a';
+	return hash % hlen;
+}
+
+/*
+ *  read a hash file with buffering
+ */
+static uchar*
+hfread(Ndbhf *hf, long off, int len)
+{
+	if(off < hf->off || off + len > hf->off + hf->len){
+		if(seek(hf->fd, off, 0) < 0
+		|| (hf->len = read(hf->fd, hf->buf, sizeof(hf->buf))) < len){
+			hf->off = -1;
+			return 0;
+		}
+		hf->off = off;
+	}
+	return &hf->buf[off-hf->off];
+}
+
+/*
+ *  return an opened hash file if one exists for the
+ *  attribute and if it is current vis-a-vis the data
+ *  base file
+ */
+static Ndbhf*
+hfopen(Ndb *db, char *attr)
+{
+	Ndbhf *hf;
+	char buf[sizeof(hf->attr)+sizeof(db->file)+2];
+	uchar *p;
+	Dir *d;
+
+	/* try opening the data base if it's closed */
+	if(db->mtime==0 && ndbreopen(db) < 0)
+		return 0;
+
+	/* if the database has changed, throw out hash files and reopen db */
+	if((d = dirfstat(Bfildes(&db->b))) == nil || db->qid.path != d->qid.path
+	|| db->qid.vers != d->qid.vers){
+		if(ndbreopen(db) < 0){
+			free(d);
+			return 0;
+		}
+	}
+	free(d);
+
+	if(db->nohash)
+		return 0;
+
+	/* see if a hash file exists for this attribute */
+	for(hf = db->hf; hf; hf= hf->next){
+		if(strcmp(hf->attr, attr) == 0)
+			return hf;
+	}
+
+	/* create a new one */
+	hf = (Ndbhf*)malloc(sizeof(Ndbhf));
+	if(hf == 0)
+		return 0;
+	memset(hf, 0, sizeof(Ndbhf));
+
+	/* compare it to the database file */
+	strncpy(hf->attr, attr, sizeof(hf->attr)-1);
+	sprint(buf, "%s.%s", db->file, hf->attr);
+	hf->fd = open(buf, OREAD);
+	if(hf->fd >= 0){
+		hf->len = 0;
+		hf->off = 0;
+		p = hfread(hf, 0, 2*NDBULLEN);
+		if(p){
+			hf->dbmtime = NDBGETUL(p);
+			hf->hlen = NDBGETUL(p+NDBULLEN);
+			if(hf->dbmtime == db->mtime){
+				hf->next = db->hf;
+				db->hf = hf;
+				return hf;
+			}
+		}
+		close(hf->fd);
+	}
+
+	free(hf);
+	return 0;
+}
+
+/*
+ *  return the first matching entry
+ */
+Ndbtuple*
+ndbsearch(Ndb *db, Ndbs *s, char *attr, char *val)
+{
+	uchar *p;
+	Ndbtuple *t;
+	Ndbhf *hf;
+
+	hf = hfopen(db, attr);
+
+	memset(s, 0, sizeof(*s));
+	if(_ndbcachesearch(db, s, attr, val, &t) == 0){
+		/* found in cache */
+		if(t != nil)
+			return t;	/* answer from this file */
+		if(db->next == nil)
+			return nil;
+		return ndbsearch(db->next, s, attr, val);
+	}
+
+	s->db = db;
+	s->hf = hf;
+	if(s->hf){
+		s->ptr = ndbhash(val, s->hf->hlen)*NDBPLEN;
+		p = hfread(s->hf, s->ptr+NDBHLEN, NDBPLEN);
+		if(p == 0)
+			return _ndbcacheadd(db, s, attr, val, nil);
+		s->ptr = NDBGETP(p);
+		s->type = Cptr1;
+	} else if(db->length > 128*1024){
+		print("Missing or out of date hash file %s.%s.\n", db->file, attr);
+	/*	syslog(0, "ndb", "Missing or out of date hash file %s.%s.", db->file, attr); */
+
+		/* advance search to next db file */
+		s->ptr = NDBNAP;
+		_ndbcacheadd(db, s, attr, val, nil);
+		if(db->next == 0)
+			return nil;
+		return ndbsearch(db->next, s, attr, val);
+	} else {
+		s->ptr = 0;
+		s->type = Dptr;
+	}
+	t = ndbsnext(s, attr, val);
+	_ndbcacheadd(db, s, attr, val, (t != nil && s->db == db)?t:nil);
+	setmalloctag(t, getcallerpc(&db));
+	return t;
+}
+
+static Ndbtuple*
+match(Ndbtuple *t, char *attr, char *val)
+{
+	Ndbtuple *nt;
+
+	for(nt = t; nt; nt = nt->entry)
+		if(strcmp(attr, nt->attr) == 0
+		&& strcmp(val, nt->val) == 0)
+			return nt;
+	return 0;
+}
+
+/*
+ *  return the next matching entry in the hash chain
+ */
+Ndbtuple*
+ndbsnext(Ndbs *s, char *attr, char *val)
+{
+	Ndbtuple *t;
+	Ndb *db;
+	uchar *p;
+
+	db = s->db;
+	if(s->ptr == NDBNAP)
+		goto nextfile;
+
+	for(;;){
+		if(s->type == Dptr){
+			if(Bseek(&db->b, s->ptr, 0) < 0)
+				break;
+			t = ndbparse(db);
+			s->ptr = Boffset(&db->b);
+			if(t == 0)
+				break;
+			if(s->t = match(t, attr, val))
+				return t;
+			ndbfree(t);
+		} else if(s->type == Cptr){
+			if(Bseek(&db->b, s->ptr, 0) < 0)
+				break; 
+			s->ptr = s->ptr1;
+			s->type = Cptr1;
+			t = ndbparse(db);
+			if(t == 0)
+				break;
+			if(s->t = match(t, attr, val))
+				return t;
+			ndbfree(t);
+		} else if(s->type == Cptr1){
+			if(s->ptr & NDBCHAIN){	/* hash chain continuation */
+				s->ptr &= ~NDBCHAIN;
+				p = hfread(s->hf, s->ptr+NDBHLEN, 2*NDBPLEN);
+				if(p == 0)
+					break;
+				s->ptr = NDBGETP(p);
+				s->ptr1 = NDBGETP(p+NDBPLEN);
+				s->type = Cptr;
+			} else {		/* end of hash chain */
+				if(Bseek(&db->b, s->ptr, 0) < 0)
+					break; 
+				s->ptr = NDBNAP;
+				t = ndbparse(db);
+				if(t == 0)
+					break;
+				if(s->t = match(t, attr, val)){
+					setmalloctag(t, getcallerpc(&s));
+					return t;
+				}
+				ndbfree(t);
+				break;
+			}
+		}
+	}
+
+nextfile:
+
+	/* nothing left to search? */
+	s->ptr = NDBNAP;
+	if(db->next == 0)
+		return 0;
+
+	/* advance search to next db file */
+	t = ndbsearch(db->next, s, attr, val);
+	setmalloctag(t, getcallerpc(&s));
+	return t;
+}