270 lines
7.7 KiB
Nim
270 lines
7.7 KiB
Nim
# nimbus-eth1
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# Copyright (c) 2021 Status Research & Development GmbH
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# Licensed under either of
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# * Apache License, version 2.0, ([LICENSE-APACHE](LICENSE-APACHE) or
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# http://www.apache.org/licenses/LICENSE-2.0)
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# * MIT license ([LICENSE-MIT](LICENSE-MIT) or
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# http://opensource.org/licenses/MIT)
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# at your option. This file may not be copied, modified, or distributed
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# except according to those terms.
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## Kvt DB -- Transaction interface
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## ===============================
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##
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{.push raises: [].}
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import
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std/[sequtils, tables],
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results,
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./kvt_desc/desc_backend,
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./kvt_desc
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func isTop*(tx: KvtTxRef): bool
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# ------------------------------------------------------------------------------
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# Private helpers
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# ------------------------------------------------------------------------------
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func getDbDescFromTopTx(tx: KvtTxRef): Result[KvtDbRef,KvtError] =
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if not tx.isTop():
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return err(TxNotTopTx)
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let db = tx.db
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if tx.level != db.stack.len:
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return err(TxStackUnderflow)
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ok db
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proc getTxUid(db: KvtDbRef): uint =
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if db.txUidGen == high(uint):
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db.txUidGen = 0
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db.txUidGen.inc
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db.txUidGen
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# ------------------------------------------------------------------------------
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# Public functions, getters
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# ------------------------------------------------------------------------------
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func txTop*(db: KvtDbRef): Result[KvtTxRef,KvtError] =
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## Getter, returns top level transaction if there is any.
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if db.txRef.isNil:
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err(TxNoPendingTx)
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else:
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ok(db.txRef)
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func isTop*(tx: KvtTxRef): bool =
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## Getter, returns `true` if the argument `tx` referes to the current top
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## level transaction.
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tx.db.txRef == tx and tx.db.top.txUid == tx.txUid
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func level*(tx: KvtTxRef): int =
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## Getter, positive nesting level of transaction argument `tx`
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tx.level
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func level*(db: KvtDbRef): int =
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## Getter, non-negative nesting level (i.e. number of pending transactions)
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if not db.txRef.isNil:
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result = db.txRef.level
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# ------------------------------------------------------------------------------
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# Public functions
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# ------------------------------------------------------------------------------
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func to*(tx: KvtTxRef; T: type[KvtDbRef]): T =
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## Getter, retrieves the parent database descriptor from argument `tx`
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tx.db
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proc forkTx*(tx: KvtTxRef): Result[KvtDbRef,KvtError] =
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## Clone a transaction into a new DB descriptor accessing the same backend
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## (if any) database as the argument `db`. The new descriptor is linked to
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## the transaction parent and is fully functional as a forked instance (see
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## comments on `kvt_desc.reCentre()` for details.)
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##
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## The new DB descriptor will contain a copy of the argument transaction
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## `tx` as top layer of level 1 (i.e. this is he only transaction.) Rolling
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## back will end up at the backend layer (incl. backend filter.)
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##
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## Use `kvt_desc.forget()` to clean up this descriptor.
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##
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let db = tx.db
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# Provide new top layer
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var topLayer: LayerRef
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if db.txRef == tx:
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topLayer = db.top.dup
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elif tx.level < db.stack.len:
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topLayer = db.stack[tx.level].dup
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else:
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return err(TxArgStaleTx)
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if topLayer.txUid != tx.txUid:
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return err(TxArgStaleTx)
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topLayer.txUid = 1
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let txClone = ? db.fork()
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# Set up clone associated to `db`
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txClone.top = topLayer # is a deep copy
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txClone.stack = @[LayerRef()]
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txClone.backend = db.backend
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txClone.txUidGen = 1
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# Install transaction similar to `tx` on clone
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txClone.txRef = KvtTxRef(
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db: txClone,
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txUid: 1,
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level: 1)
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ok(txClone)
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proc forkTop*(db: KvtDbRef): Result[KvtDbRef,KvtError] =
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## Variant of `forkTx()` for the top transaction if there is any. Otherwise
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## the top layer is cloned, only.
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##
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## Use `kvt_desc.forget()` to clean up this descriptor.
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##
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if db.txRef.isNil:
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let dbClone = ? db.fork()
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dbClone.top = db.top.dup # is a deep copy
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dbClone.backend = db.backend
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return ok(dbClone)
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db.txRef.forkTx()
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proc exec*(
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tx: KvtTxRef;
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action: KvtDbAction;
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): Result[void,KvtError] =
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## Execute function argument `action()` on a temporary `tx.forkTx()`
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## transaction database. After return, the temporary database gets
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## destroyed.
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##
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let db = ? tx.forkTx()
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db.action()
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? db.forget()
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ok()
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# ------------------------------------------------------------------------------
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# Public functions: Transaction frame
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# ------------------------------------------------------------------------------
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proc txBegin*(db: KvtDbRef): Result[KvtTxRef,KvtError] =
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## Starts a new transaction.
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##
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## Example:
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## ::
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## proc doSomething(db: KvtDbRef) =
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## let tx = db.begin
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## defer: tx.rollback()
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## ... continue using db ...
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## tx.commit()
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##
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if db.level != db.stack.len:
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return err(TxStackGarbled)
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db.stack.add db.top.dup # push (save and use top later)
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db.top.txUid = db.getTxUid()
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db.txRef = KvtTxRef(
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db: db,
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txUid: db.top.txUid,
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parent: db.txRef,
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level: db.stack.len)
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ok db.txRef
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proc rollback*(
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tx: KvtTxRef; # Top transaction on database
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): Result[void,KvtError] =
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## Given a *top level* handle, this function discards all database operations
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## performed for this transactio. The previous transaction is returned if
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## there was any.
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##
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let db = ? tx.getDbDescFromTopTx()
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# Roll back to previous layer.
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db.top = db.stack[^1]
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db.stack.setLen(db.stack.len-1)
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db.txRef = tx.parent
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ok()
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proc commit*(
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tx: KvtTxRef; # Top transaction on database
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): Result[void,KvtError] =
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## Given a *top level* handle, this function accepts all database operations
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## performed through this handle and merges it to the previous layer. The
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## previous transaction is returned if there was any.
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##
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let db = ? tx.getDbDescFromTopTx()
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# Keep top and discard layer below
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db.top.txUid = db.stack[^1].txUid
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db.stack.setLen(db.stack.len-1)
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db.txRef = tx.parent
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ok()
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proc collapse*(
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tx: KvtTxRef; # Top transaction on database
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commit: bool; # Commit if `true`, otherwise roll back
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): Result[void,KvtError] =
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## Iterated application of `commit()` or `rollback()` performing the
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## something similar to
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## ::
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## while true:
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## discard tx.commit() # ditto for rollback()
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## if db.topTx.isErr: break
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## tx = db.topTx.value
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##
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let db = ? tx.getDbDescFromTopTx()
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# If commit, then leave the current layer and clear the stack, oterwise
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# install the stack bottom.
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if not commit:
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db.stack[0].swap db.top
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db.top.txUid = 0
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db.stack.setLen(0)
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db.txRef = KvtTxRef(nil)
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ok()
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# ------------------------------------------------------------------------------
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# Public functions: save database
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# ------------------------------------------------------------------------------
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proc stow*(
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db: KvtDbRef; # Database
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): Result[void,KvtError] =
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## The function saves the data from the top layer cache into the
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## backend database.
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##
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## If there is no backend the function returns immediately with an error.
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## The same happens if there is a pending transaction.
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##
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if not db.txRef.isNil:
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return err(TxPendingTx)
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if 0 < db.stack.len:
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return err(TxStackGarbled)
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let be = db.backend
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if be.isNil:
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return err(TxBackendNotWritable)
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# Save structural and other table entries
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let txFrame = be.putBegFn()
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be.putKvpFn(txFrame, db.top.tab.pairs.toSeq)
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? be.putEndFn txFrame
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# Delete or clear stack and clear top
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db.stack.setLen(0)
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db.top = LayerRef(txUid: db.top.txUid)
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ok()
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# ------------------------------------------------------------------------------
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# End
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# ------------------------------------------------------------------------------
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