X-Git-Url: https://code.citadel.org/?p=citadel.git;a=blobdiff_plain;f=citadel%2Fserver%2Fbackends%2Fberkeley_db%2Fberkeley_db.c;h=56a5f14fb1ccfcfba63ae68d9ddfe58385ee6732;hp=ee437e0467ba1278e5764ef4a0dabe96ea05240f;hb=HEAD;hpb=0817c354e189098cd0bed910a4f503dc3c5d7f2d

diff --git a/citadel/server/backends/berkeley_db/berkeley_db.c b/citadel/server/backends/berkeley_db/berkeley_db.c
index ee437e046..56a5f14fb 100644
--- a/citadel/server/backends/berkeley_db/berkeley_db.c
+++ b/citadel/server/backends/berkeley_db/berkeley_db.c
@@ -14,9 +14,9 @@
 #include "../../sysdep.h"
 #include <sys/stat.h>
 #include <stdio.h>
-#include <dirent.h>
 #include <zlib.h>
 #include <db.h>
+#include <assert.h>
 #include <libcitadel.h>
 #include "../../citserver.h"
 #include "../../config.h"
@@ -26,9 +26,40 @@
 #error Citadel requires Berkeley DB v18.0 or newer.  Please upgrade.
 #endif
 
+// Globals (these are used across multiple functions in *this* module, but not elsewhere)
+static DB *bdb_table[MAXCDB];	// One DB handle for each Citadel database
+static DB_ENV *bdb_env;		// The DB environment (global)
 
-static DB *dbp[MAXCDB];		// One DB handle for each Citadel database
-static DB_ENV *dbenv;		// The DB environment (global)
+
+// These are items that we need to store "per thread" rather than "per session".
+struct bdb_tsd {
+	DB_TXN *tid;            // Transaction handle
+	DBC *cursors[MAXCDB];   // Cursors, for traversals...
+	DBT dbkey[MAXCDB];
+	DBT dbdata[MAXCDB];
+};
+
+
+pthread_key_t bdb_thread_key;
+#define TSD bdb_get_tsd()
+
+
+// Some functions in this backend need to store some per-thread data.
+// This returns the pointer to the current thread's per-thread data block, creating it if necessary.
+// (This will also work in a non-threaded program; it will return the same pointer every time.)
+struct bdb_tsd *bdb_get_tsd(void) {
+
+        struct bdb_tsd *c = (struct bdb_tsd *) pthread_getspecific(bdb_thread_key) ;
+	if (c != NULL) {
+		return(c);		// Got it.
+	}
+
+	// If there's no TSD for this thread, it must be a new thread.  Create our TSD region.
+	c = (struct bdb_tsd *) malloc(sizeof(struct bdb_tsd));
+	memset(c, 0, sizeof(struct bdb_tsd));
+	pthread_setspecific(bdb_thread_key, (const void *) c);
+	return(c);
+}
 
 
 // Called by other functions in this module to GTFO quickly if we need to.  Not part of the backend API.
@@ -42,7 +73,7 @@ void bdb_abort(void) {
 
 
 // Verbose logging callback for Berkeley DB.  Not part of the backend API.
-void bdb_verbose_log(const DB_ENV *dbenv, const char *msg, const char *foo) {
+void bdb_verbose_log(const DB_ENV *bdb_env, const char *msg, const char *foo) {
 	if (!IsEmptyStr(msg)) {
 		syslog(LOG_DEBUG, "bdb: %s %s", msg, foo);
 	}
@@ -50,7 +81,7 @@ void bdb_verbose_log(const DB_ENV *dbenv, const char *msg, const char *foo) {
 
 
 // Verbose error logging callback for Berkeley DB.  Not part of the backend API.
-void bdb_verbose_err(const DB_ENV *dbenv, const char *errpfx, const char *msg) {
+void bdb_verbose_err(const DB_ENV *bdb_env, const char *errpfx, const char *msg) {
 	syslog(LOG_ERR, "bdb: %s", msg);
 }
 
@@ -81,19 +112,6 @@ static void bdb_txcommit(DB_TXN *tid) {
 }
 
 
-// Wrapper for txn_begin() that logs/aborts on error.  Not part of the backend API.
-static void bdb_txbegin(DB_TXN **tid) {
-	int ret;
-
-	ret = dbenv->txn_begin(dbenv, NULL, tid, 0);
-
-	if (ret) {
-		syslog(LOG_ERR, "bdb: txn_begin: %s", db_strerror(ret));
-		bdb_abort();
-	}
-}
-
-
 // Panic callback for Berkeley DB.  Not part of the backend API.
 static void bdb_dbpanic(DB_ENV *env, int errval) {
 	syslog(LOG_ERR, "bdb: PANIC: %s", db_strerror(errval));
@@ -135,12 +153,54 @@ void bdb_check_handles(void) {
 }
 
 
+// Transaction-based stuff.  I'm writing this as I bake cookies...
+void bdb_begin_transaction(void) {
+	int ret;
+	bdb_bailIfCursor(TSD->cursors, "can't begin transaction during r/o cursor");
+
+	if (TSD->tid != NULL) {
+		syslog(LOG_ERR, "bdb: bdb_begin_transaction: ERROR: nested transaction");
+		bdb_abort();
+	}
+
+	ret = bdb_env->txn_begin(bdb_env, NULL, &TSD->tid, 0);
+	if (ret) {
+		syslog(LOG_ERR, "bdb: bdb_begin_transaction: %s", db_strerror(ret));
+		bdb_abort();
+	}
+}
+
+
+// ...and the cookies are cursed.
+void bdb_end_transaction(void) {
+	int i;
+
+	for (i = 0; i < MAXCDB; i++) {
+		if (TSD->cursors[i] != NULL) {
+			syslog(LOG_WARNING, "bdb: bdb_end_transaction: WARNING: cursor %d still open at transaction end", i);
+			bdb_cclose(TSD->cursors[i]);
+			TSD->cursors[i] = NULL;
+		}
+	}
+
+	if (TSD->tid == NULL) {
+		syslog(LOG_ERR, "bdb: bdb_end_transaction: ERROR: bdb_txcommit(NULL) !!");
+		bdb_abort();
+	}
+	else {
+		bdb_txcommit(TSD->tid);
+	}
+
+	TSD->tid = NULL;
+}
+
+
 // Request a checkpoint of the database.  Called once per minute by the thread manager.
 void bdb_checkpoint(void) {
 	int ret;
 
 	syslog(LOG_DEBUG, "bdb: -- checkpoint --");
-	ret = dbenv->txn_checkpoint(dbenv, MAX_CHECKPOINT_KBYTES, MAX_CHECKPOINT_MINUTES, 0);
+	ret = bdb_env->txn_checkpoint(bdb_env, MAX_CHECKPOINT_KBYTES, MAX_CHECKPOINT_MINUTES, 0);
 
 	if (ret != 0) {
 		syslog(LOG_ERR, "bdb: bdb_checkpoint() txn_checkpoint: %s", db_strerror(ret));
@@ -148,19 +208,15 @@ void bdb_checkpoint(void) {
 	}
 
 	// After a successful checkpoint, we can cull the unused logs
-	if (CtdlGetConfigInt("c_auto_cull")) {
-		ret = dbenv->log_set_config(dbenv, DB_LOG_AUTO_REMOVE, 1);
-	}
-	else {
-		ret = dbenv->log_set_config(dbenv, DB_LOG_AUTO_REMOVE, 0);
+	ret = bdb_env->log_set_config(bdb_env, DB_LOG_AUTO_REMOVE, 1);
+	if (ret != 0) {
+		syslog(LOG_ERR, "bdb: bdb_checkpoint() auto coll logs: %s", db_strerror(ret));
 	}
 }
 
 
-// Open the various databases we'll be using.  Any database which
-// does not exist should be created.  Note that we don't need a
-// critical section here, because there aren't any active threads
-// manipulating the database yet.
+// Open the various tables we'll be using.  Any table which does not exist should be created.  Note that we don't need a
+// critical section here, because there aren't any active threads manipulating the database yet.
 void bdb_open_databases(void) {
 	int ret;
 	int i;
@@ -183,75 +239,32 @@ void bdb_open_databases(void) {
 		exit(CTDLEXIT_DB);
 	}
 
-	// Silently try to create the database subdirectory.  If it's already there, no problem.
-	if ((mkdir(ctdl_db_dir, 0700) != 0) && (errno != EEXIST)) {
-		syslog(LOG_ERR, "bdb: database directory [%s] does not exist and could not be created: %m", ctdl_db_dir);
-		exit(CTDLEXIT_DB);
-	}
-	if (chmod(ctdl_db_dir, 0700) != 0) {
-		syslog(LOG_ERR, "bdb: unable to set database directory permissions [%s]: %m", ctdl_db_dir);
-		exit(CTDLEXIT_DB);
-	}
-	if (chown(ctdl_db_dir, CTDLUID, (-1)) != 0) {
-		syslog(LOG_ERR, "bdb: unable to set the owner for [%s]: %m", ctdl_db_dir);
-		exit(CTDLEXIT_DB);
-	}
 	syslog(LOG_DEBUG, "bdb: Setting up DB environment");
-	ret = db_env_create(&dbenv, 0);
+	ret = db_env_create(&bdb_env, 0);
 	if (ret) {
 		syslog(LOG_ERR, "bdb: db_env_create: %s", db_strerror(ret));
 		syslog(LOG_ERR, "bdb: exit code %d", ret);
 		exit(CTDLEXIT_DB);
 	}
-	dbenv->set_errpfx(dbenv, "citserver");
-	dbenv->set_paniccall(dbenv, bdb_dbpanic);
-	dbenv->set_errcall(dbenv, bdb_verbose_err);
-	dbenv->set_msgcall(dbenv, bdb_verbose_log);
-	dbenv->set_verbose(dbenv, DB_VERB_DEADLOCK, 1);
-	dbenv->set_verbose(dbenv, DB_VERB_RECOVERY, 1);
+	bdb_env->set_errpfx(bdb_env, "citserver");
+	bdb_env->set_paniccall(bdb_env, bdb_dbpanic);
+	bdb_env->set_errcall(bdb_env, bdb_verbose_err);
+	bdb_env->set_msgcall(bdb_env, bdb_verbose_log);
+	bdb_env->set_verbose(bdb_env, DB_VERB_DEADLOCK, 1);
+	bdb_env->set_verbose(bdb_env, DB_VERB_RECOVERY, 1);
 
-	// We want to specify the shared memory buffer pool cachesize, but everything else is the default.
-	ret = dbenv->set_cachesize(dbenv, 0, 64 * 1024, 0);
+	flags = DB_CREATE | DB_INIT_LOCK | DB_INIT_LOG | DB_INIT_MPOOL | DB_INIT_TXN | DB_RECOVER | DB_THREAD ;
+	syslog(LOG_DEBUG, "bdb: bdb_env->open(bdb_env, %s, %d, 0)", ctdl_db_dir, flags);
+	ret = bdb_env->open(bdb_env, ctdl_db_dir, flags, 0);				// try opening the database cleanly
 	if (ret) {
-		syslog(LOG_ERR, "bdb: set_cachesize: %s", db_strerror(ret));
-		dbenv->close(dbenv, 0);
-		syslog(LOG_ERR, "bdb: exit code %d", ret);
-		exit(CTDLEXIT_DB);
-	}
-
-	if ((ret = dbenv->set_lk_detect(dbenv, DB_LOCK_DEFAULT))) {
-		syslog(LOG_ERR, "bdb: set_lk_detect: %s", db_strerror(ret));
-		dbenv->close(dbenv, 0);
+		syslog(LOG_ERR, "bdb: bdb_env->open: %s: %s", ctdl_db_dir, db_strerror(ret));
+		bdb_env->close(bdb_env, 0);
 		syslog(LOG_ERR, "bdb: exit code %d", ret);
 		exit(CTDLEXIT_DB);
 	}
 
-	flags = DB_CREATE | DB_INIT_MPOOL | DB_PRIVATE | DB_INIT_TXN | DB_INIT_LOCK | DB_THREAD | DB_INIT_LOG;
-	syslog(LOG_DEBUG, "bdb: dbenv->open(dbenv, %s, %d, 0)", ctdl_db_dir, flags);
-	ret = dbenv->open(dbenv, ctdl_db_dir, flags, 0);				// try opening the database cleanly
-	if (ret == DB_RUNRECOVERY) {
-		syslog(LOG_ERR, "bdb: dbenv->open: %s", db_strerror(ret));
-		syslog(LOG_ERR, "bdb: attempting recovery...");
-		flags |= DB_RECOVER;
-		ret = dbenv->open(dbenv, ctdl_db_dir, flags, 0);			// try recovery
-	}
-	if (ret == DB_RUNRECOVERY) {
-		syslog(LOG_ERR, "bdb: dbenv->open: %s", db_strerror(ret));
-		syslog(LOG_ERR, "bdb: attempting catastrophic recovery...");
-		flags &= ~DB_RECOVER;
-		flags |= DB_RECOVER_FATAL;
-		ret = dbenv->open(dbenv, ctdl_db_dir, flags, 0);			// try catastrophic recovery
-	}
-	if (ret) {
-		syslog(LOG_ERR, "bdb: dbenv->open: %s", db_strerror(ret));
-		dbenv->close(dbenv, 0);
-		syslog(LOG_ERR, "bdb: exit code %d", ret);
-		exit(CTDLEXIT_DB);
-	}
-
-	syslog(LOG_INFO, "bdb: mounting databases");
 	for (i = 0; i < MAXCDB; ++i) {
-		ret = db_create(&dbp[i], dbenv, 0);					// Create a database handle
+		ret = db_create(&bdb_table[i], bdb_env, 0);				// Create a database handle
 		if (ret) {
 			syslog(LOG_ERR, "bdb: db_create: %s", db_strerror(ret));
 			syslog(LOG_ERR, "bdb: exit code %d", ret);
@@ -259,7 +272,7 @@ void bdb_open_databases(void) {
 		}
 
 		snprintf(dbfilename, sizeof dbfilename, "cdb.%02x", i);			// table names by number
-		ret = dbp[i]->open(dbp[i], NULL, dbfilename, NULL, DB_BTREE, DB_CREATE | DB_AUTO_COMMIT | DB_THREAD, 0600);
+		ret = bdb_table[i]->open(bdb_table[i], NULL, dbfilename, NULL, DB_BTREE, DB_CREATE | DB_AUTO_COMMIT, 0600);
 		if (ret) {
 			syslog(LOG_ERR, "bdb: db_open[%02x]: %s", i, db_strerror(ret));
 			if (ret == ENOMEM) {
@@ -272,26 +285,6 @@ void bdb_open_databases(void) {
 }
 
 
-// Make sure we own all the files, because in a few milliseconds we're going to drop root privs.
-void bdb_chmod_data(void) {
-	DIR *dp;
-	struct dirent *d;
-	char filename[PATH_MAX];
-
-	dp = opendir(ctdl_db_dir);
-	if (dp != NULL) {
-		while (d = readdir(dp), d != NULL) {
-			if (d->d_name[0] != '.') {
-				snprintf(filename, sizeof filename, "%s/%s", ctdl_db_dir, d->d_name);
-				syslog(LOG_DEBUG, "bdb: chmod(%s, 0600) returned %d", filename, chmod(filename, 0600));
-				syslog(LOG_DEBUG, "bdb: chown(%s, CTDLUID, -1) returned %d", filename, chown(filename, CTDLUID, (-1)));
-			}
-		}
-		closedir(dp);
-	}
-}
-
-
 // Close all of the db database files we've opened.  This can be done in a loop, since it's just a bunch of closes.
 void bdb_close_databases(void) {
 	int i;
@@ -304,38 +297,40 @@ void bdb_close_databases(void) {
 	closing = 1;
 
 	syslog(LOG_INFO, "bdb: performing final checkpoint");
-	if ((ret = dbenv->txn_checkpoint(dbenv, 0, 0, 0))) {
+	if ((ret = bdb_env->txn_checkpoint(bdb_env, 0, 0, 0))) {
 		syslog(LOG_ERR, "bdb: txn_checkpoint: %s", db_strerror(ret));
 	}
 
 	syslog(LOG_INFO, "bdb: flushing the database logs");
-	if ((ret = dbenv->log_flush(dbenv, NULL))) {
+	if ((ret = bdb_env->log_flush(bdb_env, NULL))) {
 		syslog(LOG_ERR, "bdb: log_flush: %s", db_strerror(ret));
 	}
 
 	// close the tables
 	syslog(LOG_INFO, "bdb: closing databases");
 	for (i = 0; i < MAXCDB; ++i) {
-		syslog(LOG_INFO, "bdb: closing database %02x", i);
-		ret = dbp[i]->close(dbp[i], 0);
+		ret = bdb_table[i]->close(bdb_table[i], 0);
 		if (ret) {
 			syslog(LOG_ERR, "bdb: db_close: %s", db_strerror(ret));
 		}
 	}
 
 	// Close the handle.
-	ret = dbenv->close(dbenv, DB_FORCESYNC);
+	syslog(LOG_INFO, "bdb: closing environment");
+	ret = bdb_env->close(bdb_env, DB_FORCESYNC);
 	if (ret) {
 		syslog(LOG_ERR, "bdb: DBENV->close: %s", db_strerror(ret));
 	}
+
+	syslog(LOG_INFO, "bdb: shutdown completed");
 }
 
 
-// Decompress a database item if it was compressed on disk
-void bdb_decompress_if_necessary(struct cdbdata *cdb) {
+// Decompress a DBT data block if it was compressed on disk.
+void bdb_decompress_if_necessary(DBT *d) {
 	static int magic = COMPRESS_MAGIC;
 
-	if ((cdb == NULL) || (cdb->ptr == NULL) || (cdb->len < sizeof(magic)) || (memcmp(cdb->ptr, &magic, sizeof(magic)))) {
+	if ((d == NULL) || (d->data == NULL) || (d->size < sizeof(magic)) || (memcmp(d->data, &magic, sizeof(magic)))) {
 		return;
 	}
 
@@ -349,27 +344,26 @@ void bdb_decompress_if_necessary(struct cdbdata *cdb) {
 
 	memset(&zheader, 0, sizeof(struct CtdlCompressHeader));
 	cplen = sizeof(struct CtdlCompressHeader);
-	if (sizeof(struct CtdlCompressHeader) > cdb->len) {
-		cplen = cdb->len;
+	if (sizeof(struct CtdlCompressHeader) > d->size) {
+		cplen = d->size;
 	}
-	memcpy(&zheader, cdb->ptr, cplen);
+	memcpy(&zheader, d->data, cplen);
 
-	compressed_data = cdb->ptr;
+	compressed_data = d->data;
 	compressed_data += sizeof(struct CtdlCompressHeader);
 
 	sourceLen = (uLongf) zheader.compressed_len;
 	destLen = (uLongf) zheader.uncompressed_len;
 	uncompressed_data = malloc(zheader.uncompressed_len);
 
-	if (uncompress((Bytef *) uncompressed_data,
-		       (uLongf *) &destLen, (const Bytef *) compressed_data, (uLong) sourceLen) != Z_OK) {
+	if (uncompress((Bytef *) uncompressed_data, (uLongf *) &destLen, (const Bytef *) compressed_data, (uLong) sourceLen) != Z_OK) {
 		syslog(LOG_ERR, "bdb: uncompress() error");
 		bdb_abort();
 	}
 
-	free(cdb->ptr);
-	cdb->len = (size_t) destLen;
-	cdb->ptr = uncompressed_data;
+	free(d->data);
+	d->size = (size_t) destLen;
+	d->data = uncompressed_data;
 }
 
 
@@ -385,6 +379,7 @@ int bdb_store(int cdb, const void *ckey, int ckeylen, void *cdata, int cdatalen)
 	int compressing = 0;
 	size_t buffer_len = 0;
 	uLongf destLen = 0;
+	int existing_txn = 0;			// set to nonzero if we are already inside a transaction
 
 	memset(&dkey, 0, sizeof(DBT));
 	memset(&ddata, 0, sizeof(DBT));
@@ -413,49 +408,37 @@ int bdb_store(int cdb, const void *ckey, int ckeylen, void *cdata, int cdatalen)
 	}
 
 	if (TSD->tid != NULL) {
-		ret = dbp[cdb]->put(dbp[cdb],	// db
-				    TSD->tid,	// transaction ID
-				    &dkey,	// key
-				    &ddata,	// data
-				    0		// flags
+		existing_txn = 1;
+	}
+
+	if (!existing_txn) {				// If we're not already inside a transaction,
+		bdb_begin_transaction();		// create our own for this operation.
+	}
+
+	do {
+		ret = bdb_table[cdb]->put(bdb_table[cdb],	// db
+			    	TSD->tid,			// transaction ID
+			    	&dkey,			// key
+			    	&ddata,			// data
+			    	0				// flags
 		);
-		if (ret) {
-			syslog(LOG_ERR, "bdb: bdb_store(%d): %s", cdb, db_strerror(ret));
+		if ((ret != 0) && (ret != DB_LOCK_DEADLOCK)) {
+			syslog(LOG_ERR, "bdb: bdb_store(%02x): error %d: %s", cdb, ret, db_strerror(ret));
 			bdb_abort();
 		}
-		if (compressing) {
-			free(compressed_data);
+		if (ret == DB_LOCK_DEADLOCK) {
+			syslog(LOG_DEBUG, "bdb: bdb_store(%02x): would deadlock, trying again", cdb);
 		}
-		return ret;
+	} while (ret == DB_LOCK_DEADLOCK);
+
+	if (!existing_txn) {
+		bdb_end_transaction();
 	}
-	else {
-		bdb_bailIfCursor(TSD->cursors, "attempt to write during r/o cursor");
-
-	      retry:
-		bdb_txbegin(&tid);
-
-		if ((ret = dbp[cdb]->put(dbp[cdb],	// db
-					 tid,		// transaction ID
-					 &dkey,		// key
-					 &ddata,	// data
-					 0))) {		// flags
-			if (ret == DB_LOCK_DEADLOCK) {
-				bdb_txabort(tid);
-				goto retry;
-			}
-			else {
-				syslog(LOG_ERR, "bdb: bdb_store(%d): %s", cdb, db_strerror(ret));
-				bdb_abort();
-			}
-		}
-		else {
-			bdb_txcommit(tid);
-			if (compressing) {
-				free(compressed_data);
-			}
-			return ret;
-		}
+
+	if (compressing) {
+		free(compressed_data);
 	}
+
 	return ret;
 }
 
@@ -463,134 +446,72 @@ int bdb_store(int cdb, const void *ckey, int ckeylen, void *cdata, int cdatalen)
 // Delete a piece of data.  Returns 0 if the operation was successful.
 int bdb_delete(int cdb, void *key, int keylen) {
 	DBT dkey;
-	DB_TXN *tid;
 	int ret;
+	int existing_txn = 0;				// set to nonzero if we are already inside a transaction
 
 	memset(&dkey, 0, sizeof dkey);
 	dkey.size = keylen;
 	dkey.data = key;
 
 	if (TSD->tid != NULL) {
-		ret = dbp[cdb]->del(dbp[cdb], TSD->tid, &dkey, 0);
-		if (ret) {
-			syslog(LOG_ERR, "bdb: bdb_delete(%d): %s", cdb, db_strerror(ret));
-			if (ret != DB_NOTFOUND) {
-				bdb_abort();
-			}
-		}
+		existing_txn = 1;
 	}
-	else {
-		bdb_bailIfCursor(TSD->cursors, "attempt to delete during r/o cursor");
 
-	      retry:
-		bdb_txbegin(&tid);
-
-		if ((ret = dbp[cdb]->del(dbp[cdb], tid, &dkey, 0)) && ret != DB_NOTFOUND) {
-			if (ret == DB_LOCK_DEADLOCK) {
-				bdb_txabort(tid);
-				goto retry;
-			}
-			else {
-				syslog(LOG_ERR, "bdb: bdb_delete(%d): %s", cdb, db_strerror(ret));
-				bdb_abort();
-			}
-		}
-		else {
-			bdb_txcommit(tid);
-		}
+	if (!existing_txn) {				// If we're not already inside a transaction,
+		bdb_begin_transaction();		// create our own for this operation.
 	}
-	return ret;
-}
-
 
-static DBC *bdb_localcursor(int cdb) {
-	int ret;
-	DBC *curs;
-
-	if (TSD->cursors[cdb] == NULL) {
-		ret = dbp[cdb]->cursor(dbp[cdb], TSD->tid, &curs, 0);
-	}
-	else {
-		ret = TSD->cursors[cdb]->c_dup(TSD->cursors[cdb], &curs, DB_POSITION);
+	ret = bdb_table[cdb]->del(bdb_table[cdb], TSD->tid, &dkey, 0);
+	if (ret) {
+		if (ret != DB_NOTFOUND) {
+			syslog(LOG_ERR, "bdb: bdb_delete(%02x): %s", cdb, db_strerror(ret));
+			bdb_abort();
+		}
 	}
 
-	if (ret) {
-		syslog(LOG_ERR, "bdb: bdb_localcursor: %s", db_strerror(ret));
-		bdb_abort();
+	if (!existing_txn) {
+		bdb_end_transaction();			// Only end the transaction if we began it.
 	}
 
-	return curs;
+	return ret;
 }
 
 
-// Fetch a piece of data.  If not found, returns NULL.  Otherwise, it returns
-// a struct cdbdata which it is the caller's responsibility to free later on
-// using the bdb_free() routine.
-struct cdbdata *bdb_fetch(int cdb, const void *key, int keylen) {
+// Fetch a piece of data.  Returns a "struct cdbdata"
+// If the item is not found, the pointer will be NULL.
+struct cdbdata bdb_fetch(int cdb, const void *key, int keylen) {
+
+	struct cdbdata returned_data;
+	memset(&returned_data, 0, sizeof(struct cdbdata));
 
 	if (keylen == 0) {		// key length zero is impossible
-		return(NULL);
+		return(returned_data);
 	}
 
-	struct cdbdata *tempcdb;
-	DBT dkey, dret;
+	DBT dkey;
 	int ret;
 
 	memset(&dkey, 0, sizeof(DBT));
 	dkey.size = keylen;
 	dkey.data = (void *) key;
 
-	if (TSD->tid != NULL) {
-		memset(&dret, 0, sizeof(DBT));
-		dret.flags = DB_DBT_MALLOC;
-		ret = dbp[cdb]->get(dbp[cdb], TSD->tid, &dkey, &dret, 0);
-	}
-	else {
-		DBC *curs;
-
-		do {
-			memset(&dret, 0, sizeof(DBT));
-			dret.flags = DB_DBT_MALLOC;
-			curs = bdb_localcursor(cdb);
-			ret = curs->c_get(curs, &dkey, &dret, DB_SET);
-			bdb_cclose(curs);
-		} while (ret == DB_LOCK_DEADLOCK);
-	}
-
-	if ((ret != 0) && (ret != DB_NOTFOUND)) {
-		syslog(LOG_ERR, "bdb: bdb_fetch(%d): %s", cdb, db_strerror(ret));
-		bdb_abort();
-	}
+	TSD->dbdata[cdb].flags = DB_DBT_REALLOC;
 
-	if (ret != 0) {
-		return NULL;
-	}
+	do {
+		ret = bdb_table[cdb]->get(bdb_table[cdb], TSD->tid, &dkey, &TSD->dbdata[cdb], 0);
+		if ((ret != 0) && (ret != DB_NOTFOUND) && (ret != DB_LOCK_DEADLOCK)) {
+			syslog(LOG_ERR, "bdb: bdb_fetch(%d): error %d: %s", cdb, ret, db_strerror(ret));
+			bdb_abort();
+		}
+	} while (ret == DB_LOCK_DEADLOCK);
 
-	tempcdb = (struct cdbdata *) malloc(sizeof(struct cdbdata));
-	if (tempcdb == NULL) {
-		syslog(LOG_ERR, "bdb: bdb_fetch() cannot allocate memory for tempcdb: %m");
-		bdb_abort();
-	}
-	else {
-		tempcdb->len = dret.size;
-		tempcdb->ptr = dret.data;
-		bdb_decompress_if_necessary(tempcdb);
-		return (tempcdb);
+	if (ret == 0) {
+		bdb_decompress_if_necessary(&TSD->dbdata[cdb]);
+		returned_data.len = TSD->dbdata[cdb].size;
+		returned_data.ptr = TSD->dbdata[cdb].data;
 	}
-}
-
 
-// Free a cdbdata item.
-//
-// Note that we only free the 'ptr' portion if it is not NULL.  This allows
-// other code to assume ownership of that memory simply by storing the
-// pointer elsewhere and then setting 'ptr' to NULL.  bdb_free() will then
-// avoid freeing it.
-void bdb_free(struct cdbdata *cdb) {
-	if (cdb->ptr) {
-		free(cdb->ptr);
-	}
-	free(cdb);
+	return(returned_data);
 }
 
 
@@ -604,8 +525,7 @@ void bdb_close_cursor(int cdb) {
 
 
 // Prepare for a sequential search of an entire database.
-// (There is guaranteed to be no more than one traversal in
-// progress per thread at any given time.)
+// (There is guaranteed to be no more than one traversal in progress per thread at any given time.)
 void bdb_rewind(int cdb) {
 	int ret = 0;
 
@@ -616,7 +536,7 @@ void bdb_rewind(int cdb) {
 	}
 
 	// Now initialize the cursor
-	ret = dbp[cdb]->cursor(dbp[cdb], TSD->tid, &TSD->cursors[cdb], 0);
+	ret = bdb_table[cdb]->cursor(bdb_table[cdb], TSD->tid, &TSD->cursors[cdb], 0);
 	if (ret) {
 		syslog(LOG_ERR, "bdb: bdb_rewind: db_cursor: %s", db_strerror(ret));
 		bdb_abort();
@@ -626,17 +546,18 @@ void bdb_rewind(int cdb) {
 
 // Fetch the next item in a sequential search.  Returns a pointer to a 
 // cdbdata structure, or NULL if we've hit the end.
-struct cdbdata *bdb_next_item(int cdb) {
-	DBT key, data;
-	struct cdbdata *cdbret;
+struct cdbkeyval bdb_next_item(int cdb) {
+	struct cdbkeyval kv;
 	int ret = 0;
 
-	// Initialize the key/data pair so the flags aren't set.
-	memset(&key, 0, sizeof(key));
-	memset(&data, 0, sizeof(data));
-	data.flags = DB_DBT_MALLOC;
+	memset(&kv, 0, sizeof(struct cdbkeyval));
 
-	ret = TSD->cursors[cdb]->c_get(TSD->cursors[cdb], &key, &data, DB_NEXT);
+	// reuse memory from the previous call.
+	TSD->dbkey[cdb].flags = DB_DBT_REALLOC;
+	TSD->dbdata[cdb].flags = DB_DBT_REALLOC;
+
+	assert(TSD->cursors[cdb] != NULL);
+	ret = TSD->cursors[cdb]->c_get(TSD->cursors[cdb], &TSD->dbkey[cdb], &TSD->dbdata[cdb], DB_NEXT);
 
 	if (ret) {
 		if (ret != DB_NOTFOUND) {
@@ -644,51 +565,16 @@ struct cdbdata *bdb_next_item(int cdb) {
 			bdb_abort();
 		}
 		bdb_close_cursor(cdb);
-		return NULL;	// presumably, end of file
-	}
-
-	cdbret = (struct cdbdata *) malloc(sizeof(struct cdbdata));
-	cdbret->len = data.size;
-	cdbret->ptr = data.data;
-	bdb_decompress_if_necessary(cdbret);
-
-	return (cdbret);
-}
-
-
-// Transaction-based stuff.  I'm writing this as I bake cookies...
-void bdb_begin_transaction(void) {
-	bdb_bailIfCursor(TSD->cursors, "can't begin transaction during r/o cursor");
-
-	if (TSD->tid != NULL) {
-		syslog(LOG_ERR, "bdb: bdb_begin_transaction: ERROR: nested transaction");
-		bdb_abort();
+		return(kv);		// presumably, we are at the end
 	}
 
-	bdb_txbegin(&TSD->tid);
-}
-
-
-void bdb_end_transaction(void) {
-	int i;
+	bdb_decompress_if_necessary(&TSD->dbdata[cdb]);
 
-	for (i = 0; i < MAXCDB; i++) {
-		if (TSD->cursors[i] != NULL) {
-			syslog(LOG_WARNING, "bdb: bdb_end_transaction: WARNING: cursor %d still open at transaction end", i);
-			bdb_cclose(TSD->cursors[i]);
-			TSD->cursors[i] = NULL;
-		}
-	}
-
-	if (TSD->tid == NULL) {
-		syslog(LOG_ERR, "bdb: bdb_end_transaction: ERROR: bdb_txcommit(NULL) !!");
-		bdb_abort();
-	}
-	else {
-		bdb_txcommit(TSD->tid);
-	}
-
-	TSD->tid = NULL;
+	kv.key.len = TSD->dbkey[cdb].size;
+	kv.key.ptr = TSD->dbkey[cdb].data;
+	kv.val.len = TSD->dbdata[cdb].size;
+	kv.val.ptr = TSD->dbdata[cdb].data;
+	return (kv);
 }
 
 
@@ -701,27 +587,21 @@ void bdb_trunc(int cdb) {
 		syslog(LOG_ERR, "bdb: bdb_trunc must not be called in a transaction.");
 		bdb_abort();
 	}
-	else {
-		bdb_bailIfCursor(TSD->cursors, "attempt to write during r/o cursor");
 
-	      retry:
-
-		if ((ret = dbp[cdb]->truncate(dbp[cdb],	// db
-					      NULL,	// transaction ID
-					      &count,	// #rows deleted
-					      0))) {	// flags
-			if (ret == DB_LOCK_DEADLOCK) {
-				goto retry;
-			}
-			else {
-				syslog(LOG_ERR, "bdb: bdb_truncate(%d): %s", cdb, db_strerror(ret));
-				if (ret == ENOMEM) {
-					syslog(LOG_ERR, "bdb: You may need to tune your database; please read http://www.citadel.org for more information.");
-				}
-				exit(CTDLEXIT_DB);
-			}
+	bdb_begin_transaction();				// create our own transaction for this operation.
+	ret = bdb_table[cdb]->truncate(bdb_table[cdb],		// db
+				      NULL,			// transaction ID
+				      &count,			// #rows deleted
+				      0);			// flags
+								//
+	if (ret) {
+		syslog(LOG_ERR, "bdb: bdb_truncate(%d): %s", cdb, db_strerror(ret));
+		if (ret == ENOMEM) {
+			syslog(LOG_ERR, "bdb: You may need to tune your database; please read http://www.citadel.org for more information.");
 		}
+		exit(CTDLEXIT_DB);
 	}
+	bdb_end_transaction();
 }
 
 
@@ -733,7 +613,7 @@ void bdb_compact(void) {
 	syslog(LOG_DEBUG, "bdb: bdb_compact() started");
 	for (i = 0; i < MAXCDB; i++) {
 		syslog(LOG_DEBUG, "bdb: compacting database %d", i);
-		ret = dbp[i]->compact(dbp[i], NULL, NULL, NULL, NULL, DB_FREE_SPACE, NULL);
+		ret = bdb_table[i]->compact(bdb_table[i], NULL, NULL, NULL, NULL, DB_FREE_SPACE, NULL);
 		if (ret) {
 			syslog(LOG_ERR, "bdb: compact: %s", db_strerror(ret));
 		}
@@ -742,8 +622,25 @@ void bdb_compact(void) {
 }
 
 
+// periodically called for maintenance
+void bdb_tick(void) {
+	int ret;
+	int rejected;
+
+	ret = bdb_env->lock_detect(bdb_env, 0, DB_LOCK_DEFAULT, &rejected);
+	if (ret) {
+		syslog(LOG_ERR, "bdb: lock_detect: %s", db_strerror(ret));
+	}
+	else if (rejected) {
+		syslog(LOG_DEBUG, "bdb: rejected lock %d", rejected);
+	}
+}
+
+
 // Calling this function activates the Berkeley DB back end.
 void bdb_init_backend(void) {
+
+	// Assign the backend API stubs to the functions in this module.
 	cdb_compact = bdb_compact;
 	cdb_checkpoint = bdb_checkpoint;
 	cdb_rewind = bdb_rewind;
@@ -752,16 +649,20 @@ void bdb_init_backend(void) {
 	cdb_close_databases = bdb_close_databases;
 	cdb_store = bdb_store;
 	cdb_delete = bdb_delete;
-	cdb_free = bdb_free;
 	cdb_next_item = bdb_next_item;
 	cdb_close_cursor = bdb_close_cursor;
 	cdb_begin_transaction = bdb_begin_transaction;
 	cdb_end_transaction = bdb_end_transaction;
 	cdb_check_handles = bdb_check_handles;
 	cdb_trunc = bdb_trunc;
-	cdb_chmod_data = bdb_chmod_data;
+	cdb_tick = bdb_tick;
+
+	// Some functions in this backend need to store some per-thread data.
+	// We create the key here, during module initialization.
+	if (pthread_key_create(&bdb_thread_key, NULL) != 0) {
+		syslog(LOG_ERR, "pthread_key_create() : %m");
+		exit(CTDLEXIT_THREAD);
+	}
 
 	syslog(LOG_INFO, "db: initialized Berkeley DB backend");
 }
-
-