Whether Ratio Decidendi is overlooked by the Legislature or not ?

The Author is Devendra Pratap Singh, pursuing law from Amity University, Lucknow Campus.

Ratio decidendi is the legal basis upon which a court’s opinion is based. This could be related to any number of sources — statutes, legal texts, ethical opinions, and (of course) other courts’ opinions.
Stare decisis is the principle that once a court has decided a matter, that decision shall stand and all courts of inferior jurisdiction must follow that decision.
For example, the ratio decidendi of Roe v. Wade was basically that the Constitutionally-protected “penumbra” of rights includes a woman’s right to take medical decisions about her own body, including abortion. Stare decisis applies from that point forward to other inferior and equal courts’ opinions on the subject — so another court couldn’t just rule that abortion could be banned because that would overrule the opinion of the superior court.
Where it gets “messy” is when a court overrules a prior opinion, upsetting the principle of stare decisis — based on a ratio decidendi that the old case no longer applies for whatever legal reason may be explained.
Ratio decidendi is the reasoning that brings the court to its conclusion.
Stare decisis is the principle of not overturning previous rulings to maintain predictability and stability in the law.

In a Low Level Common Law Court, under what circumstances is it allowed to not follow precedent?
By "low level common law court," I assume you mean a state trial court in a state that has adopted the common law (as I think every state except Louisiana has).
There are two essential kinds of precedent: binding precedents and persuasive precedents.  Binding precedent consists of opinions by the state courts of appeals and state courts of last resort to which the trial court is subject, so long as they haven't been reversed or superseded by new statutes or constitutional amendments.  Decisions of the U.S. district court, court of appeals, and Supreme Court are also binding on questions of federal law or the U.S. Constitution, but not on questions of state law.  The trial court may not ignore binding precedents; should it try to do so, the court of appeals will reverse the decision, and could potentially even discipline the judge if he was knowingly and blatantly defying clearly applicable binding precedents.
All other court opinions are persuasive: the decisions of courts of other states or foreign nations, federal court decisions from other circuits, federal court decisions from the trial court's own circuit that interpret and apply state law, and the trial court's own previous decisions in other cases.  The court may follow persuasive precedents, and often will, but it doesn't have to.  A question on which there is no binding precedent is sometimes called a "case of first impression."  Often the persuasive precedents will contradict each other.  If the trial court ignores the persuasive precedent and the loser appeals, the court of appeals will often side with the trial court.
Actually lawyers and courts rarely speak of binding "precedents" alone, but about binding "authority," which also includes applicable statutes, constitutional provisions, treaties, executive orders, regulations and higher court rules.  "Precedent" usually means only a prior judicial opinion, and is only one kind of authority.  New statutes or constitutional amendments often override precedents.

Can judicial decisions be considered as a source of law?
The main sources of law in India are the Constitution, statutes, customary law and case law.
Article 141 of the Indian Constitution explicitly states that Law declared by Supreme Court to be binding on all courts. The law declared by the Supreme Court shall be binding on all courts within the territory of India.
The doctrine of Stare Decisis which means following the precedent on a point of law is also incorporated in the Indian Constitution.
Any decision made by a High Court shall be binding on the subordinate courts of that district. The same decision shall not be binding on other High Courts. Basically  two High Courts can have a difference of opinion on the same question of Law.
Most importantly, a decision of the Supreme Court shall be treated as a precedent only if it decides the question of LAW.
Under International Law
Article 38 of the Statute of the International Court of Justice deals with sources of International Law.
Article 38(1) (d) states that judicial decisions a primary source of international law. It has persuasive value for the Court to decide further cases on the same point of law.
Hence under the Indian Law and International Law, Judicial Decisions can be regarded as sources of Law.

 Can Indian Supreme Court turn down the legislation passed by the government? Which was the famous legislation turned down by Supreme Court of India?
 Yes, SC has the power to turn down the legislation made by parliament, if it violates the fundamental rights or in case it is against the basic structure doctrine
For ex SC held that National judicial appointment commission is violative and needs to be repealed because it was against the independence of judiciary which constitutes basic structure of Indian constitution.
The Judicial review is the power of the Supreme Court to examine the constitutionality of legislative enactments and executive orders of both the central and state governments. The judicial review is needed to uphold the principle of the supremacy of the Constitution, to maintain the concept of federalism (balance between the central and state governments) and also to protect the fundamental rights of the citizens.
But the words “Judicial Review” is not mentioned in the Constitution. The Supreme Court used the power of judicial review in
Golaknath Case – 1967
Bank Nationalization case – 1970
The Privy purses abolition case - 1971
The Kesavananda Bharti case – 1973
The Minerva Mills case - 1980
Second, the basic feature doctrine. This means any legislative enactment which is altering the basic feature of the constitution can be struck down by the Supreme Court.
Basic features - independent judiciary, secularism, parliamentary democracy, welfare state etc.
In a collective order, on 16 October 2015 the Supreme Court had struck down the NJAC Act, 2014 meant to replace the two-decade old collegium system of judges appointing judges in the higher judiciary as it was challenging the independence of judiciary.
It’s not fixed whether RATIO DECIDENDI is over looked by the LEGISLATION and vice versa but if any one of them violates the fundamental right or in any case it is against the basic structure doctrine then the amendment will be made in the case of law.